Office of Water

EPA 815-D-15-001

October 2015

Draft - Technologies for Legionella Control:

Scientific Literature Review
Office of Water (4607M)

EPA 815-D-15-001 

October 2015 
This page intentionally left blank. 
Disclaimer 

This draft document was prepared by the U.S. Environmental Protection Agency (EPA) as a 

technical resource for primacy agencies, building water system operators, and building owners to 

consider as they evaluate technologies to respond to the risks associated with Legionella

colonization of premise plumbing. This draft document is a summary of publicly available, peerreviewed, technical literature that evaluates the effectiveness of six technologies used for 

Legionella control. The draft document also discusses water quality issues that could result when 

using the various approaches, and summarizes operational conditions for each technology. It also 

discusses critical multiple-barrier approaches to address microbial (including Legionella), 

physical and chemical risks in various parts of the building water system, such as water 

management programs (WMPs), hazard analysis and critical control point (HACCP), and water 

safety plans (WSPs). This document also provides an overview of other strategies that primacy 

agencies, building water system operators, and building owners could consider when addressing 

threatening public health risks associated with a legionellosis outbreak. 

This draft document is not a regulation; it is not legally enforceable; and it does not confer legal 

rights or impose legal obligations on any party, including EPA, states or the regulated 

community. While EPA has made every effort to ensure the accuracy of any references to 

statutory or regulatory requirements, the obligations of the interested stakeholders are 

determined by statutes, regulations or other legally binding requirements, not this document. In 

the event of a conflict between the information in this document and any statute or regulation, 

this document would not be controlling. 

Although this document describes technologies for controlling Legionella in finished water, the 

information presented may not be appropriate for all situations and alternative approaches may 

be applicable. 

Mention of trade names or commercial products does not constitute an EPA endorsement or 

recommendation for use.
Draft – Technologies for Legionella Control: 

Scientific Literature Review i October 2015 

Table of Contents

Table of Contents ........................................................................................................................... i

Table of Exhibits .......................................................................................................................... iii

Abbreviations and Acronyms ..................................................................................................... iv

Acknowledgements ...................................................................................................................... vi

Preface .......................................................................................................................................... vii

Executive Summary ...................................................................................................................... 1

1 Background ............................................................................................................................ 2

1.1 Purpose and Scope .................................................................................................................2

1.2 Legionella: Overview ............................................................................................................2

1.2.1 General Information ...................................................................................................... 2

1.2.2 Epidemiology and Pathogenesis .................................................................................... 3

1.2.3 Ecology and Physiology ................................................................................................ 5

1.3 Legionella Occurrence and Risk from the Distribution System and Building Water 

System ...................................................................................................................................6

1.4 Regulatory Context ................................................................................................................7

2 Multi-Barrier Approaches and Technologies to Control Legionella ................................ 8

2.1 Overview of Current State of Knowledge .............................................................................8

2.2 Multi-Barrier Approaches ...................................................................................................10

2.2.1 Background ................................................................................................................. 10

2.2.2 Applications of Multi-Barrier Approaches .................................................................. 11

2.2.3 Environmental Testing ................................................................................................ 12

2.3 Technologies .......................................................................................................................13

2.3.1 Chlorine ....................................................................................................................... 13

2.3.1.1 Background ......................................................................................................... 13

2.3.1.2 Characterization of Effectiveness against Legionella ......................................... 14

2.3.1.3 Potential Water Quality Issues ............................................................................ 19

2.3.1.4 Operational Conditions ........................................................................................ 20

2.3.2 Monochloramine ......................................................................................................... 21

2.3.2.1 Background ......................................................................................................... 21

2.3.2.2 Characterization of Effectiveness against Legionella ......................................... 22

2.3.2.3 Potential Water Quality Issues ............................................................................ 27

2.3.2.4 Operational Conditions ........................................................................................ 28

2.3.3 Chlorine Dioxide ......................................................................................................... 30

2.3.3.1 Characterization of Effectiveness against Legionella ......................................... 30

2.3.3.2 Potential Water Quality Issues ............................................................................ 33

2.3.3.3 Operational Conditions ........................................................................................ 34

2.3.4 Copper-Silver Ionization ............................................................................................. 36

2.3.4.1 Background ......................................................................................................... 36

2.3.4.2 Characterization of Treatment Technology Effectiveness against Legionella .... 36

2.3.4.3 Potential Water Quality Issues ............................................................................ 38

2.3.4.4 Operational Conditions ........................................................................................ 39
Draft – Technologies for Legionella Control: 

Scientific Literature Review ii October 2015 

2.3.5 Ultraviolet Light Disinfection ..................................................................................... 41

2.3.5.1 Background ......................................................................................................... 41

2.3.5.2 Characterization of Effectiveness against Legionella ......................................... 42

2.3.5.3 Potential Water Quality Issues ............................................................................ 43

2.3.5.4 Operational Conditions ........................................................................................ 44

2.3.6 Ozone ........................................................................................................................... 45

2.3.6.1 Background ......................................................................................................... 45

2.3.6.2 Characterization of Effectiveness against Legionella ......................................... 45

2.3.6.3 Potential Water Quality Issues ............................................................................ 47

2.3.6.4 Operational Conditions ........................................................................................ 47

3 Other Strategies Used to Control for Legionella .............................................................. 49

3.1 Emergency Remediation .....................................................................................................49

3.1.1 Superheat-and-Flush Disinfection ............................................................................... 49

3.1.1.1 Background ......................................................................................................... 49

3.1.1.2 Characterization of Effectiveness against Legionella ......................................... 49

3.1.1.3 Potential Water Quality Issues ............................................................................ 51

3.1.1.4 Operational Conditions ........................................................................................ 52

3.1.2 Shock Hyperchlorination ............................................................................................. 53

3.1.2.1 Background ......................................................................................................... 53

3.1.2.2 Characterization of Effectiveness Against Legionella ........................................ 53

3.1.2.3 Potential Water Quality Issues ............................................................................ 54

3.1.2.4 Operational Conditions ........................................................................................ 55

3.2 Point-of-Use Filtration ........................................................................................................55

3.2.1 Background ................................................................................................................. 55

3.2.2 Characterization of Effectiveness against Legionella ................................................. 57

3.2.3 Potential Water Quality Issues .................................................................................... 59

3.2.4 Operational Conditions ................................................................................................ 59

4 Questions and Answers on Legionella Control in Building Water Systems .................. 60

4.1 Public Health Concerns .......................................................................................................60

4.2 Potential Regulatory Requirements .....................................................................................60

4.3 Control Measures ................................................................................................................62

4.4 New Technology Approval .................................................................................................64

4.5 Permitting ............................................................................................................................64

4.6 Sampling and Monitoring ....................................................................................................65

4.7 Operator Certification ..........................................................................................................66

4.8 Unintended Consequences ..................................................................................................67

4.9 Additional Sources of Information ......................................................................................67

5 References ............................................................................................................................ 68

A Appendix .............................................................................................................................. 93

A.1 Elements of Hazard Analysis and Critical Control Points (HACCP) .................................93

A.2 Elements of a Water Management Program ........................................................................96

A.3 Elements of Water Safety Plan ............................................................................................97
Draft – Technologies for Legionella Control: 

Scientific Literature Review iii October 2015 

Table of Exhibits

Exhibit 1-1: Legionella transmission ....................................................................................... 4

Exhibit 2-1: Kuchta et al. (1983) findings on CT values (min-mg/L) for 2-log (99 percent) 

reduction of L. pneumophila using chlorine ..................................................... 15

Exhibit 2-2: Jacangelo et al. (2002) findings on CT values (min-mg/L) for 2-log (99 percent) 

reduction of L. pneumophila using chlorine ..................................................... 15

Exhibit 2-3: UV doses (mJ/cm2) for inactivation of L. pneumophila .................................... 43

Exhibit 3-1: Membrane filtration guide for removal of microbial contaminants .................. 56
Draft – Technologies for Legionella Control: 

Scientific Literature Review iv October 2015 

Abbreviations and Acronyms

ANSI American National Standards Institute

AOC Assimilable organic carbon

ASHRAE American Society of Heating, Refrigerating and Air-Conditioning Engineers 

ATP Adenosine triphosphate 

AWWA American Water Works Association 

C Celsius

CDC Centers for Disease Control and Prevention 

CFR Code of Federal Regulations

CFU Colony-forming units

CSI Copper/silver ionization 

CT The product of disinfectant residual concentration “C” and contact time “T” 

(C × T)

DBP Disinfection byproduct 

DBPR Disinfectants and Disinfection Byproducts Rule 

DPD N,N-diethyl-p-phenylenediamine 

EPA United States Environmental Protection Agency 

F Fahrenheit

FIFRA Federal Insecticide, Fungicide and Rodenticide Act 

GWR Ground Water Rule 

HAA Haloacetic acid

HAA5 Sum of the mass concentrations of five haloacetic acid species

HACCP Hazard analysis and critical control points 

HPC Heterotrophic plate count 

ICP/MS Inductively coupled plasma/mass spectrometry

ICU Intensive care unit

km Kilometers

MCL Maximum contaminant level

MF Microfiltration

mg/L Milligrams per liter

mJ/cm2 Millijoule per square centimeter

mM Millimolar

MRDL Maximum residual disinfectant level

NDMA N-nitrosodimethylamine

NF Nanofiltration 

OSHA Occupational Safety and Health Administration

POE Point-of-entry 

POU Point-of-use

ppm Parts per million

PWS Public water system

qPCR Quantitative polymerase chain reaction

RO Reverse osmosis

SDWA Safe Drinking Water Act

SMCL Secondary maximum contaminant level
Draft – Technologies for Legionella Control: 

Scientific Literature Review v October 2015 

spp. All species within a genus

SWTR Surface Water Treatment Rule

THM Trihalomethane 

TTHM Total trihalomethane

μ Micron (millionth of a weight, distance and/or volume unit) 

μg/L Micrograms per liter

μm Micrometer

UF Ultrafiltration 

U.S. United States

UV Ultraviolet

UVT UV transmittance

VBNC Viable but non-culturable 

WHO World Health Organization

WMP Water management programs

WSG Water supply guidance

WSP Water safety plan
Draft – Technologies for Legionella Control: 

Scientific Literature Review vi October 2015 

Acknowledgements

EPA’s Office of Ground Water and Drinking Water would like to thank the Association of State

Drinking Water Administrators; the States of Maryland, Minnesota, Nevada, New York, Ohio, 

Pennsylvania, Washington; and the U.S. Centers for Disease Control for their contributions to this 

document. EPA thanks these participants for their meaningful input which was critical for the 

development of this draft document.

The following individuals helped to develop and/or review this draft document: 

César Cordero (U.S. EPA)

1

Mike Finn (U.S. EPA)

1

Tom Grubbs (U.S. EPA)

1 

Hannah Holsinger (U.S. EPA)

1

Crystal Rodgers-Jenkins (U.S. EPA)

1

Lili Wang (U.S. EPA)

1

Stacy Pfaller (U.S. EPA)

1 

Darren Lytle (U.S. EPA)

1 

Mark Rodgers (U.S. EPA)

1

Jennifer Carr (Nevada Department of 

Environmental Protection)1

Ross Cooper (Nevada Department of 

Environmental Protection)

1

David Dziewulski (New York State 

Department of Health)

1

Samuel Perry (Washington State 

Department of Health)

1

Darrell Osterhoudt, (Association of 

State Drinking Water 

Administrators)

Laurel Garrison (CDC)

Natalia A. Kozak-Muiznieks (CDC)

Claressa Lucas (CDC)

Leslie Darman (U.S. EPA) 

Phil Berger (U.S. EPA) 

Stig Regli (U.S. EPA) 

Ken Rotert (U.S. EPA) 

John Hebert (U.S. EPA) 

Jingrang Lu (U.S. EPA) 

Emily Mitchell (U.S. EPA) 

Mark Perry (U.S. EPA) 

Jonathan Pressman (U.S. EPA) 

Nicole Shao (U.S. EPA) 

Alysa Suero (U.S. EPA) 

Elizabeth Messer (Ohio EPA)

Jerry Smith (Minnesota Department 

of Health) 

Lloyd Wilson (New York State 

Department of Health) 

Nick Codru (New York State 

Department of Health) 

Lisa Daniels (Pennsylvania 

Department of Environmental 

Protection) 

Saeid Kasraei (Maryland Department 

of the Environment) 

Michael Elovitz (U.S. EPA) 

1

Lead author
Draft – Technologies for Legionella Control: 

Scientific Literature Review vii October 2015 

Preface

This draft document is a compilation of publicly available, peer-reviewed, technical literature 

that evaluates the effectiveness of technologies to control for Legionella. The United States 

Environmental Protection Agency (EPA) developed this document because the agency 

recognizes that Legionella is a public health threat. EPA also recognizes that many facility 

managers are choosing to install treatment systems to prevent or mitigate Legionella in their 

building’s plumbing systems. The agency expects this document will help to further improve 

public health by helping the targeted audience make science-based, risk management decisions 

regarding treatment and control of Legionella in buildings. The EPA is not promoting or 

endorsing treatment technologies as a preferred means of Legionella control. Rather the agency 

seeks to provide decision makers with scientific information on the effectiveness of these 

technologies and the operational requirements. The target audience for this document includes, 

but is not limited to, primacy agencies, building water system operators, building owners and 

technology developers and vendors. 

The intent of this document is to provide a summary of scientific information on Legionella

control technologies that may be considered when assessing a particular building water 

system(s). The EPA did not evaluate individual study quality with the goal of making 

recommendations for or against the use of any of the technologies discussed in the document. 

The scientific information presented in this draft document comes from published literature 

related to six technologies used for Legionella control (chlorine, monochloramine, chlorine 

dioxide, copper-silver ionization (CSI), ultraviolet (UV) disinfection and ozone). The draft 

document also discusses water quality issues that could result when using the various 

approaches, and it summarizes operational conditions for each technology. It also discusses 

critical multi-barrier approaches for addressing microbial, physical and chemical risks in various 

parts of the building water system, such as water management programs (WMPs), hazard 

analysis and critical control point (HACCP), and water safety plans (WSPs). This document also 

provides an overview of other strategies that primacy agencies, building water system operators 

and building owners could consider when addressing a public health threat such as a legionellosis 

outbreak. 

The EPA developed this draft document in collaboration with state co-regulators. Legionella

subject matter experts at the Centers for Disease Control and Prevention (CDC) reviewed and 

provided feedback on portions of the draft document. All parties were invited to compile the 

peer-reviewed literature referenced in this document. The scientific information in this document 

spans from the 1970s to 2014 and is limited to peer-reviewed literature. Information published in 

trade journals or popular magazines is not included in this document. 

There is not a single one-size-fits-all approach to addressing Legionella concerns in all building 

water systems. A determination of which strategy is best suited for a particular building water 

system is case-specific due in part to the complex and diverse nature of building water systems. 

This document does not recommend the addition of treatment nor the installation of any of the 

technologies discussed herein, but rather provides technical information, based on the publicly 
Draft – Technologies for Legionella Control: 

Scientific Literature Review viii October 2015 

available, peer-reviewed literature, about technologies and other approaches for controlling 

Legionella and other microbial contaminants. In some facilities, risks associated with the 

building water system (including Legionella) may be addressed without the addition of 

treatment. 

Stakeholders (e.g., primacy agencies, technology developers and vendors) who are interested in 

information about the approval process for a new or alternative drinking water treatment 

technology are advised to consult EPA’s Water Supply Guidance (WSG) 90, “State Alternative 

Technology Approval Protocol” (USEPA, 1996). The goal of WSG 90 is to provide a 

streamlined and consistent protocol to facilitate state approval of new drinking water treatment 

technologies. WSG 90 is not meant to replace current state plan review and approval processes. 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 1 October 2015 

Executive Summary

[This is a placeholder. The Executive Summary will be drafted after comments from the public 

and expert peer review have been incorporated.]
Draft – Technologies for Legionella Control: 

Scientific Literature Review 2 October 2015 

1 Background

1.1 Purpose and Scope

The purpose of this document is to characterize the current body of knowledge regarding the 

effectiveness of available technologies for the control of Legionella in building finished drinking 

water systems (building water systems).

1

 Throughout this document the term building water 

system refers to the pipe infrastructure inside a building used to deliver finished drinking water 

intended for human consumption. The U.S. Environmental Protection Agency (EPA) defines 

water “intended for human consumption” as water used for drinking, bathing, showering, hand 

washing, teeth brushing, food preparation, dishwashing, and maintaining oral hygiene (40 CFR 

141.801). Discussions of Legionella control issues related to cooling towers are not within the 

scope of this document. The EPA developed this document in collaboration with state coregulators. Legionella subject matter experts at the Centers for Disease Control (CDC) reviewed 

and provided feedback on portions of the draft document. All parties were invited to compile the 

peer-reviewed literature that is summarized and referenced in this document. 

The agency expects this document will help to further improve public health by helping the 

primacy agencies,2 building water system operators, building owners, technology developers and 

vendors make science-based risk management decisions regarding treatment and control of 

Legionella in buildings. The EPA is not promoting or endorsing treatment technologies as a 

preferred means of Legionella control in buildings. Rather, the agency seeks to provide decision 

makers with scientific information on the effectiveness of these technologies and the operational 

requirements. The EPA did not evaluate individual study quality or the body of evidence from 

available studies with the goal of making recommendations for or against the use of any of the 

technologies discussed in the document. 

1.2 Legionella: Overview

1.2.1 General Information 

The genus Legionella currently includes more than 50 bacterial species and approximately 70 

distinct serogroups, many of which are considered pathogenic (DSMZ, 2014; LPSN, 2014; 

Pearce et al., 2012; Bartram et al., 2007; Fields et al., 2002). Legionella pneumophila was the 

first species to be described following an outbreak of pneumonia in 1976 among members of the 

American Legion, who were attending a convention in Philadelphia, Pennsylvania (Fields et al., 

2002; McDade et al., 1979). Approximately half of the Legionella species described to date have 

been associated with clinical cases of legionellosis (any disease caused by Legionella), but it is 

likely that most Legionellae can cause human disease under the appropriate conditions (Borella 

 

1 For the purposes of this document, the term “Legionella” refers to the genus Legionella (any species). The plural 

form Legionellae and Legionella spp. are also used to denote the genus Legionella. 2 Primacy – States and Indian Tribes are given primary enforcement responsibility (e.g., primacy) for public water 

systems in their State if they meet certain requirements.
Draft – Technologies for Legionella Control: 

Scientific Literature Review 3 October 2015 

et al., 2005; Fields, 1996; Fang et al., 1989). There are several EPA regulations that provide 

some degree of protection against Legionella (see Section 1.4 for additional information). 

Legionellae are gram-negative, rod-shaped bacteria. Legionellosis is acquired by inhaling or 

aspirating aerosolized water or soil (potting soil, compost soil) contaminated with Legionella 

(Travis et al., 2012), as opposed to person-to-person contact, animal-to-person transmission,

consumption of contaminated food, or ingestion of contaminated water. Though animals can be 

infected by Legionella and develop disease, they have not been identified as carriers of 

Legionella, nor has transmission from animals to humans been documented (Cunha, 2006; 

USEPA, 1999a).

1.2.2 Epidemiology and Pathogenesis 

Legionellosis includes Legionnaires’ disease, characterized by pneumonia (Fraser et al., 1977), 

and Pontiac fever, a milder flu-like illness without pneumonia (Kaufmann et al., 1981; Glick et 

al., 1978). Hospitalization and intensive care is common among Legionnaires’ disease patients; 

inpatient costs are estimated at $433 million per year, with a case fatality rate of 5–30 percent

(Collier et al., 2012). The economic costs associated with loss of productivity and death are not 

included in these estimates and are likely to be significant. 

Legionellosis is a nationally notifiable disease, which means that any case that is confirmed by a 

laboratory is reported to CDC by state health departments (CDC, 2005). However, many cases of 

pneumonia that could be Legionnaires’ disease are empirically treated with antibiotics and never 

tested for Legionella, so the incidence could be much higher than reported (CDC, 2011; Marston 

et al., 1997). Between 3,000 and 4,000 cases of legionellosis are reported to CDC each year; 

however, the actual number of hospitalized cases is estimated to be between 8,000 and 18,000 

(CDC, 2013a; CDC, 2012; Marston et al., 1997). 

In the United States, waterborne disease outbreaks associated with Legionella have been tracked 

through the Waterborne Disease and Outbreak Surveillance System since 2001 (Craun et al., 

2010). Between 2009 and 2010, CDC reported that Legionella accounted for 19 of the 33 

drinking water-related waterborne disease outbreaks in the United States, causing 72 illnesses 

and 8 deaths. Environmental conditions within building water systems were identified as the 

cause of 11 of the 19 Legionella outbreaks (CDC, 2013b). 

Strains of L. pneumophila belonging to serogroup 1 are responsible for most legionellosis cases 

in the United States and Europe (Borella et al., 2005; Yu et al., 2002; Fields et al., 2002; Marston 

et al., 1994). L. pneumophila serogroup 6 may be the second most common serogroup, based on 

the frequency with which it is isolated from clinical samples (Marston et al., 1994). 

Although L. pneumophila causes most cases of Legionnaires’ disease, other species can also 

cause the disease, particularly in hospital-acquired cases. Of the reported non-L. pneumophila

infections, the most common causes of infection are L. micdadei, L. bozemanii, L. dumoffii and

L. longbeachae (Fang et al., 1989; Reingold et al., 1984). 

While anyone can develop Legionnaires’ disease, factors associated with an increased risk of 

developing infection include age (>50 years), gender (male), smoking and drinking habits, 

existing lung conditions (e.g., asthma, chronic obstructive pulmonary disease), 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 4 October 2015 

immunosuppressed or immunocompromised status (e.g., persons receiving transplants or 

chemotherapy, those with kidney disease, diabetes or AIDS), and recent surgery or intubation 

(Health Canada, 2013; Newton et al., 2010; Bartram et al., 2007; Stout and Yu, 1997).

Exhibit 1-1 shows different factors and events that could affect the transmission of Legionella in 

environmental and clinical settings. Legionellosis outbreaks can occur when Legionellae

multiply under particular conditions in water systems and the water is then aerosolized and 

subsequently inhaled or aspirated by susceptible persons (Donohue et al., 2014; Fields et al., 

2002; Blatt et al., 1993; Stout et al., 1985; Fliermans et al., 1981). For these reasons, the presence 

of Legionella is a particular concern in large buildings that house susceptible populations, such 

as facilities in the healthcare and hospitality industries (Health Canada, 2013; Williams et al., 

2013; Buse and Ashbolt, 2012; CDC, 2008; Rusin et al., 1997; Colbourne and Dennis, 1989). 

However, recent outbreaks have demonstrated that legionellosis infections are not limited to 

those environments. 

Exhibit 1-1: Legionella transmission

Source: ASHRAE, 2000

Building water systems can be colonized with Legionella and transmit the bacteria through 

showerheads, faucets, whirlpool spas, respiratory therapy devices, ultrasonic mist machines, 

humidifiers, cooling towers, decorative fountains and industrial-use water (Haupt et al., 2012; 

Wallensten et al., 2010; Carducci et al., 2010; Edelstein, 2007; Stout and Yu, 1997; CDC, 1997; 

Blatt et al., 1993; Addiss et al., 1989; Muder et al., 1986; Bollin et al., 1985; Dondero et al.,

1979; Glick et al., 1978). Cases have also been linked to ice machines, windshield washer fluid 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 5 October 2015 

and birthing pools (Public Health England, 2014; Wallensten et al., 2010; Nagai et al., 2003; 

Franzin et al., 2001; Graman et al., 1997). In addition, several infections have been linked to 

exposures to potting soil (Whiley and Bentham, 2011; CDC, 2000). 

1.2.3 Ecology and Physiology 

Fresh water is the major natural reservoir for Legionellae. The bacteria are found worldwide in 

many different natural aquatic environments (e.g., lakes, rivers and groundwater); however, 

exposure to these sources typically does not result in legionellosis. Legionella species have also 

been found to occur in natural soil, potting soil and compost samples (van Heijnsbergen et al., 

2014; Travis et al., 2012; CDC, 2000).

Legionella exhibit several properties that allow them to persist in extreme environmental 

conditions such as low and high temperatures, presence of disinfectants, low pH, low nutrients 

and high salinity (Health Canada, 2013; Borella et al., 2005; Kuchta et al., 1983; Fliermans et al., 

1981). Ideal growth conditions are in warm water between 35 and 46 degrees Celsius (C) (95–

114.8 degrees Fahrenheit (F)) (Buse and Ashbolt, 2011; Katz and Hammel, 1987; Wadowsky et 

al., 1985; Yee and Wadowsky, 1982; Dondero et al., 1979; Glick et al., 1978). High relative 

humidity increases the viability of Legionella species in contaminated aerosols (Heng et al., 

1995). Legionellae are considered thermotolerant bacteria, able to withstand temperatures of 50 

degrees C (122 degrees F) for several hours (Bartram et al., 2007). This characteristic allows 

Legionella species to occur frequently in heated water systems (Taylor et al., 2009). Legionella

species can also survive at temperatures below 20 degrees C (68 degrees F) and even below 

freezing (Borella et al., 2005). 

Legionella species are often found to be protected from adverse environmental conditions as a 

result of their association with biofilms, as well as their symbiotic and parasitic interactions with 

other microorganisms. The association of L. pneumophila with many different microorganisms 

in aqueous environments has been widely demonstrated. Studies have shown the ability of 

Legionella to parasitize and multiply in several species of protozoa including amoebae, ciliated 

protozoa and slime mold (Cervero-Aragó et al., 2014; Escoll et al., 2013; Buse et al., 2013; Buse 

and Ashbolt, 2011; Taylor et al., 2009; Fields, 1996) as well as establish symbiotic interactions 

with other bacteria (Taylor et al., 2009; Rowbotham, 1986; Wadowsky et al., 1985; Bohach and

Snyder, 1983; Wadowsky and Yee, 1983; Fliermans et al., 1981). The ability of Legionella

species to parasitize certain protozoa that are commonly found to graze on biofilms in 

distribution systems is considered particularly important in their ability to survive and grow

under adverse environmental conditions (Hoffman et al., 2014; Escoll et al., 2013; Richards et 

al., 2013; Bartram et al., 2007; Hwang et al., 2007; Molmeret et al., 2004; Storey et al., 2004a; 

Storey et al., 2004b; Thomas et al., 2004; Fields et al., 1984). Legionella can parasitize alveolar 

macrophages (white blood cells that are part of the immune system) in human lungs the same

way it parasitizes protozoa (Hoffman et al., 2014). 

Multiple studies suggest that protozoa play a major role in the transmission of L. pneumophila

and subsequently, legionellosis. Some of the research indicates that infectivity may be 

substantially increased if amoebae infected by Legionella are inhaled, as opposed to individual 

free-living Legionella cells (Richards et al., 2013; Newton et al., 2010; Borella et al., 2005; 

Cirillo et al., 1999; Brieland et al., 1996). Infected amoebae may contain hundreds of Legionella 

cells, which, when released from the amoeba, could allow a large number of bacteria to reach the 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 6 October 2015 

lungs (Buse and Ashbolt, 2012; Ohno et al., 2008; Berk et al., 1998; Kwaik et al., 1998; O’Brien 

and Bhopal, 1993). A study by Berk et al. (1998) also showed that protozoa can release vesicles 

(membrane-bound, sack-like structures within a cell) of respirable size containing live L. 

pneumophila. The vesicles are resistant to freeze-thawing and sonication (a procedure that uses 

sound waves to break cells), and the bacteria within the vesicles are highly resistant to biocides.

Another survival mechanism of Legionella spp. is their ability to enter a viable but not culturable 

(VBNC) state. Bacteria in a VBNC state fail to grow on culture media, where they would 

normally grow, yet are still alive and could cause disease (Oliver, 2010). Numerous chemical 

and environmental factors have been reported to induce a VBNC state, including nutrient 

starvation, extreme temperatures, high salt concentrations, low oxygen concentration, heavy 

metals and chemical treatment (including water disinfection) (Ducret et al., 2014; Alleron et al., 

2013; Oliver, 2010; Kana et al., 2008; Colbourne and Dennis, 1989). Studies suggest that 

bacteria in the VBNC state can maintain their infectivity, multiply in their hosts and recover their

ability to grow on solid media (Ducret et al., 2014; Alleron et al., 2013; Oliver, 2010; Steinert et 

al., 1997). 

1.3 Legionella Occurrence and Risk from the Distribution System and Building

Water System 

Building water systems have been identified as sources of Legionella infection (Stout et al., 

1992; Muder et al., 1986), particularly through exposure via showers and hot water systems. 

Within healthcare facilities such as hospitals and nursing homes drinking water is the most 

common source of exposure (Lin et al., 2011a). Exposure to Legionella has also been associated 

with other types of building water systems (e.g., hotels and other buildings with complex water 

distribution systems) (Silk et al., 2012; Hung et al., 1993; Tobin et al., 1981a and 1981b). 

L. pneumophila has been found in the biofilms of water mains in distribution systems, although 

proliferation has not been shown (Armon et al., 1997; States et al., 1990). Legionella spp. are 

known to occur in finished water from water treatment plants and therefore, drinking water is 

known to be a source of Legionella found in building water systems (Donohue et al., 2014; 

Schaechter et al., 1998). Section 1.2.3 discusses optimal conditions for Legionella growth in the 

distribution system. 

Several surveys have found Legionella in building water systems, including buildings that had 

not been linked to recognized outbreaks: 

• Donohue et al. (2014) used two quantitative polymerase chain reaction (qPCR)3 assays to 

evaluate incidence of L. pneumophila serogroup 1 in 272 water samples collected in 2009 

and 2010 from 68 public and private cold drinking water taps across the United States. L. 

pneumophila serogroup 1 was detected in 47 percent of the taps. 

 

3 A quantitative polymerase chain reaction assay detects a specific gene target known to be associated with a 

specific genus/species/serogroup but it cannot distinguish between viable and nonviable cells (Donohue et al., 2014).
Draft – Technologies for Legionella Control: 

Scientific Literature Review 7 October 2015 

• Wadowsky et al. (1985) found that naturally occurring L. pneumophila multiplied at a 

temperature between 25 and 37 degrees C, at pH levels of 5.5 to 9.2, and at 

concentrations of dissolved oxygen of 6.0 to 6.7 mg/L. 

• Wadowsky et al. (1982) sampled showerheads, shower pipes, and water and sediment 

collected from the bottom of hot water tanks in 11 buildings, including five homes and 

three hospitals. L. pneumophila serogroups 1, 5 and 6 were isolated from the drinking 

water fixtures in seven buildings including 1 of the 5 homes. Legionellae were also 

present in water and sediment in hot water tanks maintained at temperatures from 39 to 

54 degrees C (102.2 to 129.2 degrees F), but not found in tanks maintained between 71 

and 77 degrees C (between 159.8 and 170.6 degrees F). The authors hypothesized that hot 

water tanks are the major source and seed of L. pneumophila in building water systems.

• Tobin et al. (1981b) conducted a survey of 31 building water systems in hospitals and 

hotels, 6 of which were associated with sporadic cases or outbreaks of Legionnaires’ 

disease. For the 6 buildings (hospitals and hotels) associated with cases of Legionnaires’ 

disease, the study found L. pneumophila in all of the building water systems and in the 

cooling water for each of the 3 buildings with cooling towers. For buildings that had not 

previously experienced an outbreak, the study found L. pneumophila in 4 out of 24 taps 

or showers, 3 out of 9 cooling towers, and 1 out of 15 storage tanks. 

1.4 Regulatory Context 

EPA regulates Legionella under the Surface Water Treatment Rule (SWTR). The SWTR has 

treatment technique requirements to control for Giardia and viruses. The SWTR’s treatment 

technique requirements presume that if sufficient treatment is provided to control for Giardia

and viruses (i.e., 3-log inactivation of Giardia and 4-log inactivation of viruses), then Legionella

risks will also be controlled. In addition, the Revised Total Coliform Rule and the Ground Water 

Rule have treatment technique requirements that address bacteria, which provide some control of 

Legionella. All of these rules apply to public water systems (PWSs). 

Building water systems may or may not be subject to federal drinking water regulations under 40 

CFR Part 141. States and/or local governments may have drinking water standards for such 

systems even if federal regulations do not apply. To ensure adequate public health protection, 

federal and state oversight may be needed since adding certain technologies in a building water 

system could impact the chemical and microbial quality of the water within the system. The EPA 

issued guidance that primacy agencies may use as they make regulatory implication decisions 

(USEPA, 1976, USEPA, 1990). 

A determination of which technology is best suited for a particular building water system is casespecific in part due to the complex and diverse nature of building water systems. This document 

does not recommend the addition of treatment nor the installation of any of the technologies 

discussed herein; however, it does provide information regarding the operational requirements

that regulated PWSs must comply with. This information is included only to provide the reader 

with a comprehensive understanding of the technologies. 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 8 October 2015 

Building owners who are considering adding treatment to their building water systems may wish 

to consult with their water supplier (i.e., PWS) to better understand any potential water quality

issues before making treatment related decisions. If a decision to add treatment to the building 

water system seems likely, EPA advises building owners to consult with their primacy agency 

for any specific requirements that may apply before they add any treatment. 

2 Multi-Barrier Approaches and Technologies to Control Legionella

2.1 Overview of Current State of Knowledge

The following sections of this document describe multi-barrier approaches and technologies for 

controlling Legionella in building water systems. The information presented is based on the 

references reviewed during the preparation of this document. Section 2.2 introduces multi-barrier 

approaches as a framework for identifying and prioritizing hazards within a particular building 

water system and determining the specific control measures for each priority hazard. Section 2.3

introduces several commercially available technologies that show some effectiveness in 

mitigating potential exposure to Legionella in building water systems, including chlorine, 

monochloramine, chlorine dioxide, copper/silver ionization (CSI), ultraviolet (UV) light 

disinfection and ozone. For each technology, the document provides background information, 

general characterization of its effectiveness against Legionella, potential water quality issues, 

and operational conditions (including monitoring frequency and location). This document does 

not rank or recommend any one technology over another. The information in Section 2.3 is 

presented in the context of national drinking water requirements. Applicability of such 

requirements to a building water system would need to be determined by the building water 

system operator in consultation with the primacy agency and/or water supplier. 

In Section 3, other strategies (i.e., remediation methods) are discussed, including emergency 

superheat-and-flush disinfection, shock hyperchlorination and point-of-use (POU) filtration. This

section summarizes what is currently known about the performance of these individual 

technologies for controlling the occurrence of Legionella bacteria and other waterborne 

pathogens in buildings. 

In general, all of the technologies discussed in this document have been shown to offer some 

degree of effectiveness against Legionella. However, the long-term eradication of Legionella

from a building water system has not been demonstrated consistently with any of these

technologies. Complex plumbing systems, such as those found in a multi-story building, may 

have areas where there is less exposure to disinfectants, which could provide opportunities for 

bacteria to grow. Legionella bacteria can be found in biofilms or in stagnant sections of the 

plumbing system. The effectiveness of a technology against Legionella in biofilm or Legionella

ingested by amoebae is often cited as a concern. 

The maintenance of a disinfectant residual throughout the system is critical for the effectiveness 

of chlorine, monochloramine, chlorine dioxide and CSI treatments. Maintaining a disinfectant 

residual provides increased protection in the event Legionella is released into the building water 

system (e.g., sloughing off of biofilm material containing Legionella) or enters a building water 

system through the PWS distribution system. Ozone and UV disinfection do not produce a 

disinfectant residual. Therefore, water treated with these methods, in some cases, may be 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 9 October 2015 

susceptible to subsequent contamination. For these reasons, more than one type of treatment or 

control measure may be necessary to inhibit Legionella growth in a building water system

(Department of Veterans Affairs, 2014). The use of multi-barrier approaches is further discussed 

in Section 2.2. 

The effectiveness of a particular technology is dependent upon building-specific characteristics 

such as pipe material, age and condition; water usage rates and water age; and water quality 

parameters (e.g., pH, hardness, organic contaminants, inorganic contaminants, types of 

waterborne pathogens). Therefore, decision makers may want to consider the specific conditions 

of each building water system before making a decision and ensure that the conditions are 

adequate for the selected approach. 

The physical and chemical characteristics of the finished water have an impact on the 

effectiveness of all the treatment technologies discussed, albeit not to the same degree. For 

example, chlorine and chlorine dioxide disinfectant residuals may be difficult to maintain as the 

water temperature increases due to faster reaction with organic materials or pipe surfaces. In 

contrast, temperature has little impact on the effectiveness of copper or silver ions. The pH of the 

finished water will significantly impact the effectiveness of chlorine, monochloramine and 

copper and silver ions, but it will have less of an impact on the effectiveness of chlorine dioxide. 

Other physical parameters (such as turbidity) and chemical constituents (such as chlorides and 

dissolved organic carbon) can also affect the performance of specific technologies. These issues 

are covered in more detail in Section 2.3. 

Ensuring proper maintenance is a priority for all of the technologies discussed. Failures of 

technologies put in place to protect building inhabitants from exposure to Legionella have 

resulted in outbreaks (CDC, 2013b). Safety concerns also exist for most of the technologies 

(USEPA, 1999b, 1999c). The use of strong oxidants such as chlorine requires proper handling to 

avoid adverse health risks. The Stage 1 Disinfection Byproduct Rule (DBPR) requires PWSs 

using chlorine, monochloramine and chlorine dioxide to maintain disinfection byproduct (DBP) 

concentrations below levels that can cause negative human health implications (USEPA, 1998; 

Rohr et al., 1999; States et al., 1998). These water quality issues are discussed in Section 2.3. 

Unless a legionellosis outbreak occurs, the decision to employ additional treatment is often 

difficult for building owners. Some building owners choose to install supplemental disinfection 

treatment systems as a preventative measure based on economic, insurance or marketing reasons. 

The detection of Legionella bacteria in finished water samples from a building is likely the most 

common reason some facilities may choose to add treatment. 

The CDC does not recognize a safe level of Legionella and recommends certain preventative and 

corrective actions in health facilities that care for patients who are at higher risk for Legionella

infection (CDC, 2003). However, because of the ubiquitous nature of environmental Legionella, 

a robust response to every positive test result is likely unnecessary and could be both costly and 

damaging to the building infrastructure. Outbreaks of legionellosis have occurred when this 

metric was applied. In some instances, risks associated with the building water system (including 

Legionella) can be addressed by taking measures other than the addition of treatment after 

careful analysis of the particular conditions of the building water system. Thus, decision makers 

may want to consider the specific conditions of a building water system to better inform 

decisions made in response to detection of Legionella. Multi-barrier approaches commonly 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 10 October 2015 

include consideration of parameters such as the building water system layout, water processes

such as heating and water softening, methods of transmission such as showers and spas, and the 

risk level of the potentially exposed population based on age and immune status. 

2.2 Multi-Barrier Approaches

2.2.1 Background 

Multi-barrier approaches refer to programs that systematically apply risk management principles 

to reduce biological (including Legionella), chemical and physical risks associated with building 

water systems. Different names are used throughout the literature to describe multi-barrier 

approaches. Some examples of multi-barrier approaches include water management programs 

(WMPs), hazard analysis and critical control point programs (HACCP), and water safety plans 

(WSPs).

The HACCP concept was established in the early 1960s by The Pillsbury Company in 

coordination with the National Aeronautic and Space Administration and the U.S. Army 

Laboratories. It was created to ensure the safety of food from microbiological hazards for 

astronauts working in space (Mortimore and Wallace, 2001). Beginning in the mid-1970s, 

HACCP principles were applied to the food industry as a preventative approach for addressing 

biological, chemical and physical hazards. This approach to food safety was recognized by WHO 

as being essential for controlling foodborne disease. In 1993, the Codex Alimentarius 

Commission food code, established by the Food and Agriculture Organization of the United 

Nations and the World Health Organization (WHO), adopted the HACCP approach (FAO, 

1998). After seeing the success of HACCP in the food industry, water utilities began to 

implement the HACCP approach. The process for using HACCP in a water system was 

originally described within a food journal, Food Control, in 1994 (Havelaar, 1994). 

HACCP can be viewed as a continuous multi-barrier approach for protecting finished water and 

building water systems from hazards that may occur. While many water systems use some 

aspects of the HACCP approach, implementing a full HACCP program that evaluates an entire 

system in detail ensures the highest level of public health protection (Deere and Davison, 1998). 

WSPs are also considered a comprehensive risk-management approach; WSPs use multiple 

barriers to ensure public health protection from the source to the tap (WHO, 2011). The use of 

HACCP in the water industry was the basis for the development of WSPs by the WHO (Figueras

and Borrego, 2010; WHO, 2005). 

The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) 

Standard 188 describes a multi-barrier approach that establishes minimum legionellosis risk 

management requirements for building water systems. ASHRAE uses the term water 

management programs to describe the multi-barrier approach (ASHRAE, 2015). 

The application of any multi-barrier approaches, such as WMP, HACCP or WSPs can be 

beneficial for water systems and building water systems in protecting water quality and public 

health in general. For more information on WMPs please refer to the ASHRAE Standard 188 

(ASHRAE, 2015). For more information on WSPs, the reader is referred to WHO documents 

(WHO 2011; WHO 2005). For information about the HACCP, WMP and WSP elements
Draft – Technologies for Legionella Control: 

Scientific Literature Review 11 October 2015 

elements, see the Appendix of this document. Slight variations can be observed in the elements 

or steps described by each approach. The EPA does not make any specific recommendation 

regarding the use of any particular approach. The EPA advises building water system operators 

and owners to determine which approaches may be more suitable to their specific needs or 

whether a combination of approaches is appropriate. 

2.2.2 Applications of Multi-Barrier Approaches

Water system managers have found success in implementing multi-barrier approaches such as 

WMP, HACCP and WSP, similar to the successes seen in the food industry for many years. In 

1999, Brisbane, Australia, employed HACCP as a means of protecting the water treatment 

process, storage and distribution system (Gray and Morain, 2000). A system in Melbourne, 

Australia, implemented HACCP in 1999 and improved outcomes including streamlined work 

procedures, a net decrease in customer complaints, and a better understanding of the quality 

issues (Mullenger et al., 2002). Five full-scale HACCP applications in Australian water 

distribution systems resulted in reductions in customer complaints and water quality incidents. 

Other improvements attributed to HACCP were noted in work processes, documentation and 

recordkeeping, and the system’s capability to demonstrate due diligence. Pilot-scale applications 

in U.S. distribution systems showed that HACCP was feasible and practical, but the time and 

resource requirements for implementing the plans were greater than expected (Martel et al., 

2006). Researchers in Japan have concluded that HACCP ensures safe and high quality drinking 

water; they also have proven success with safe water through the previous uses of HACCP for 

bottled water and ice production (Yokoi at al., 2006). In Iceland, an estimated 68 percent of the 

population consumes drinking water from systems with WSPs. In a 2008 evaluation of water 

systems, the authors noted that compliance with drinking water standards improved considerably 

upon implementation of HACCP (Gunnarsdóttir and Gissurarson, 2008). 

Implementing multi-barrier risk management concepts for building water systems has also been 

shown to be successful. The Occupational Safety and Health Administration (OSHA) recognizes 

the importance of having controls for building water systems in place, as under the right 

conditions any water source can be a source of disease and illness (OSHA, 1999). ASHRAE also 

recognizes the importance of risk management for building water systems in its Standard 188, 

Legionellosis: Risk Management for Building Water Systems (ASHRAE, 2015). NSF 

International is developing a draft standard based on application of HACCP to building water 

systems for Legionella control. In addition to applying multi-barrier risk management concepts 

to existing building water systems, building designers can also use these concepts in the design 

phase for new building water systems to help reduce and control hazards (Krageschmidt et al., 

2014). 

Multi-barrier approaches have proven to be effective for controlling the growth of significant 

pathogens in building water systems (Gillilland et al., 2014), as documented in the following 

case studies: 

• In 2004, a university clinic in Germany adopted the WSP concept based on HACCP. One

immediate success this clinic noted was the correction of an infrastructural failure that

was identified during the process. Three years after implementation, two additional

improvements were noted: a lowered rate of sepsis in very low birth weight neonates and
Draft – Technologies for Legionella Control: 

Scientific Literature Review 12 October 2015 

no cases of nosocomial (hospital-acquired) Legionnaires’ disease since implementation 

(Dyck et al., 2007). 

• In Minnesota, the Mayo Clinic used HACCP principles to build a water management 

program for its multi-campus healthcare facilities. During implementation of HACCP the 

clinic found distribution piping design issues and determined that additional hazard 

controls were needed. The water management program improved the awareness of water 

quality issues (Krageschmidt et al., 2014). 

• Evaluations of outbreaks of Legionnaires’ disease have shown system deficiencies to be 

contributing factors to outbreaks (CDC, 2013b). The implementation of HACCP plans or 

WSPs may identify and help to correct these deficiencies. 

In addition to applying multi-barrier risk management concepts to existing building water 

systems, building designers can also use these concepts in the design phase for new building 

water systems to help reduce and control hazards (Krageschmidt et al., 2014). For example, 

designing a system to minimize water age and dead-end pipelines may limit the occurrence of 

waterborne pathogens. Another example is to exclude the use of decorative fountains which can 

be a source of Legionella; the Veterans Administration has concluded that they should not be 

included in healthcare interior designs (Department of Veterans Affairs, 2012). 

Addition of treatment as part of a multi-barrier approach into a building water system’s operation 

and maintenance program could have regulatory implications. The EPA advises building owners

who are considering adding treatment to consult with their water supplier and primacy agency 

for any specific considerations or requirements that may apply. 

2.2.3 Environmental Testing

Environmental testing involves collecting water samples from the building water system and 

analyzing for L. pneumophila or other hazards of concern, as well as for water quality parameters 

(pH, temperature, disinfectant residual) that may indicate efficacy of treatment performance and 

overall water quality. Environmental testing may be performed in the context of an outbreak 

investigation in order to determine the source and stop transmission or as part of a multi-barrier 

Legionella prevention plan such as a WMP, HACCP or WSP (ASHRAE, 2015; Sidari et al., 

2014; Kozak et al., 2013). 

Using Legionella test results as a measure of risk for disease transmission is problematic due to 

many knowledge gaps, including but not limited to, infectious dose, efficiency of aerosolgenerating devices, susceptibility of potential hosts, and virulence of the strain. While detection 

of Legionella in a building water system may indicate conditions conducive to Legionella 

persistence, it is also clear from worldwide studies that the strains of Legionella most often 

detected during routine environmental testing are rarely the strains that cause disease (KozakMuiznieks et al., 2014; Euser et al., 2013; Harrison et al., 2009, Kozak et al., 2009; Doleans et 

al., 2004). The lack of reliable and definitive human infectious dose information for Legionella

makes environmental monitoring results difficult to translate into action levels that can directly 

reduce human health risks (Buse et al., 2012; Schoen and Ashbolt, 2011; Storey et al., 2004a; 

Storey et al., 2004b; O’Brien and Bhopal, 1993; Fitzgeorge et al., 1983). 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 13 October 2015 

Guidelines on routine environmental testing for Legionella vary among different agencies, 

including the Veterans Health Administration (VHA), CDC, and WHO (Barker et al., 2015). 

VHA recommends routine environmental testing for Legionella in VHA facilities (VHA, 2014). 

CDC and WHO recognize that environmental Legionella counts alone cannot predict the 

probability of human infection from a water system because other factors, such as the exposure 

dose and level of host susceptibility, contribute to the likelihood of infection (Bartram et al., 

2007; Sehulster and Chinn, 2003). Despite the limitations of environmental monitoring, WHO 

continues to recommend using Legionella testing as one way to validate a WSP (Bartram et al., 

2007). Similarly, a WMP or HACCP approach for protecting a building water system might 

involve routinely monitoring water temperature, disinfectant residual levels, and the functioning 

of any other treatment system, leaving the more complicated testing for Legionella for validation 

of the plan being used. Current challenges to environmental testing for Legionella include the 

following: 

• Despite a number of published procedures for the detection of Legionella in water 

samples, standard culture methods remain limited by their sensitivity and unreliability in

detecting a wide range of Legionella spp. on a consistent basis (Buse et al., 2012) and

detecting VBNC Legionella (Oliver, 2010). Further, the time it takes to receive results

limits the utility of testing. 

• Wide fluctuations occur in Legionella testing results from the same tap on a daily basis 

and from the same water sample between laboratories (Lucas et al., 2011).

• There is a lack of standardized protocols for the selection of sampling sites and the 

frequency of sampling (Lucas et al., 2011; Bartram et al., 2007). 

If a decision is made to conduct routine environmental testing for Legionella as part of a multibarrier approach, a building-specific sampling plan should be developed that specifies the 

location of sampling sites, the type of samples, the frequency of sampling, the sample collection

method and the sample analysis method (Krageschmidt et al., 2014). However, there is no 

consensus on how many and which types of samples to take (e.g., bulk water or biofilm), nor 

how often to perform the sampling in order to accurately assess the risk from Legionella. 

2.3 Technologies

2.3.1 Chlorine 

2.3.1.1 Background 

Chlorine and chlorine-based compounds are disinfectants that can serve the dual role of 

efficiently inactivating microorganisms during water treatment, as well as maintaining the 

quality of the water as it flows from the treatment plant to the consumer’s tap (Calomoris and 

Christman, 1998). Chlorine is a powerful oxidant that effectively inactivates a large variety of 

microbial waterborne pathogens, including those that can cause typhoid fever, dysentery, cholera 

and Legionnaires’ disease.
Draft – Technologies for Legionella Control: 

Scientific Literature Review 14 October 2015 

Chlorine is added to drinking water as elemental chlorine (chlorine gas), sodium hypochlorite 

solution or dry calcium hypochlorite. Chlorine as sodium hypochlorite is the form of disinfectant 

most often applied in buildings (Rosenblatt and McCoy, 2014). Chlorine can be applied by 

facilities for routine treatment of both hot and cold domestic water; it can be applied to the cold 

and hot water tanks or to the entire distribution system. Chlorine can also be used at high doses 

for emergency disinfection of potable water systems through shock chlorination (also called 

shock hyperchlorination). Shock chlorination is covered in more detail in Section 3.1.2.

For chlorine to be effective against microorganisms, it must be present in sufficient 

concentration, and it must have adequate time to react (Calomoris and Christman, 1998). This 

combination of concentration and reaction time is expressed as C (mg/L) × T (min), or CT. For 

continued protection against potentially harmful organisms in distribution systems or building 

water systems, some level of chlorine needs to be maintained after the initial application. The 

remaining chlorine is known as residual chlorine. 

The addition of chlorine to water creates two chemical species that together make up “free 

chlorine.” These species, hypochlorous acid (HOCl, electrically neutral) and hypochlorite ion 

(OCl-

, electrically negative), behave very differently. Hypochlorous acid is more reactive than 

the hypochlorite ion and is also the stronger disinfectant and oxidant. The ratio of hypochlorous 

acid to hypochlorite ion in water is determined by pH. At low pH (6–7), hypochlorous acid 

dominates, while at high pH (>8.5) the hypochlorite ion dominates. Thus, the pH of the incoming 

water may be a factor when deciding upon the use of chlorine as a disinfectant, or in the 

engineering design when addressing issues such as CT for the target organism(s). 

Chlorine was first used as a primary disinfectant of drinking water in Jersey City, New Jersey, in 

1908. Chlorine is widely credited with virtually eliminating outbreaks of waterborne disease in 

the United States and other developed countries (Calomoris and Christman, 1998). The use of 

chlorine to control microbes has the lowest production and operating costs of any disinfectant, as 

well as the longest history for large continuous disinfection operations. Among PWSs that

disinfect, chlorine is the most commonly used disinfectant (AWWA Disinfection Systems 

Committee, 2008).

2.3.1.2 Characterization of Effectiveness against Legionella

Both laboratory and full-scale studies have been conducted to assess the effectiveness of chlorine 

against Legionella. These studies included a range of physical and chemical water conditions 

such as chlorine dose and residual levels, temperature and pH. Lin et al. (2002) reviewed 

available literature on the efficacy of various disinfectants against Legionella; findings related to 

chlorine disinfection include the following: 

o Relatively high doses of chlorine (2–6 mg/L) were needed for continuous control 

of Legionella in water systems. 

o The effectiveness of chlorine increased with temperature, although chlorine 

residual decay also increased. 

o The association of Legionella with protozoa required much higher doses of 

chlorine for inactivation. Lin et al. (2002) noted that this association with 

protozoa may explain why chlorine can suppress Legionella in water systems but 

cannot usually prevent regrowth of Legionella. 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 15 October 2015 

The laboratory studies that follow examined the effectiveness of chlorine in inactivating 

Legionella under a range of pH, temperature and chlorine residual levels. Results showed a wide 

range of CT values needed for all inactivation levels.

• Kuchta et al. (1983) studied the effects of various chlorine concentrations, temperatures 

and pH levels on Legionella in tap water. The chlorine residuals used (0.1 and 0.5 mg/L) 

were consistent with residual levels that would be expected in PWSs. The ranges of pH 

and temperature conditions evaluated are shown in Exhibit 2-1. Results show that lower 

CT is required for higher temperature and lower pH. The authors noted that contact times 

for the clinical and other environmental sources of Legionella were as long as, or longer, 

than those required for river samples, although long contact times were needed regardless 

of serogroup or origin. The authors concluded that low chlorine concentrations (0.1 

mg/L) allowed Legionella to survive for relatively long periods of time. Increasing the 

total chlorine concentration predictably enhanced the bactericidal effect, resulting in a 99 

percent (2-log) kill within the first 5 minutes at a concentration of 0.5 mg/L.

Exhibit 2-1: Kuchta et al. (1983) findings on CT values (min-mg/L) for 2-log (99

percent) reduction of L. pneumophila using chlorine

Temperature in degrees C 

(in degrees F) pH 6.0 pH 7.0 pH 7.6

4 (39.2) 6–9

21 (69.8) 0.5 1–6 4

32 (89.6) 3.2 <3

Source: Kuchta et al. (1983)

• Jacangelo et al. (2002) conducted laboratory studies to examine the efficacy of current 

disinfection practices (e.g., chlorine dioxide, free chlorine and monochloramine) for 

inactivation of waterborne emerging pathogens including Legionella. Chlorine doses of 

1.0 to 4.0 mg/L were used. Three different temperatures (5, 15 and 25 degrees C, or 41, 

59 and 77 degrees F, respectively) and three different pH (6.0, 7.0 and 8.0) values were 

examined. Results are presented as CT (min-mg/L) values. The observed CT values for 

2-log (99 percent) reduction of L. pneumophila are shown in Exhibit 2-2. These CT 

values were at least an order of magnitude higher than those reported by Kuchta et al. 

(1983). The wide range of CT values reported in the literature could be due to different 

water quality conditions and test protocols used for inactivating Legionella. 

Exhibit 2-2: Jacangelo et al. (2002) findings on CT values (min-mg/L) for 2-log (99

percent) reduction of L. pneumophila using chlorine

Temperature in degrees C 

(in degrees F) pH 6.0 pH 7.0 pH 8.0

5 (41) >50 to >320 50 to 250 250 to >1,000

15 (59) 100 to >320 60 to >320 25 to >710

25 (77) 40 to 500 100 to 160 130 to 250

Source: Jacangelo et al. (2002)
Draft – Technologies for Legionella Control: 

Scientific Literature Review 16 October 2015 

The following pilot studies evaluated the efficacy of chlorine disinfection for inactivating

Legionella without co-occurring microbial organisms. Both studies were completed using warm 

water conditions. 

• Muraca et al. (1987) compared chlorine, heat, ozone and UV for inactivating Legionella

in a model building water system. A suspension of Legionella was added to the system 

and allowed to circulate. Chlorine disinfection consisted of maintaining a residual 

concentration between 4 and 6 mg/L by multiple additions of chlorine. Chlorine 

experiments were conducted at 25, 43 and 45 degrees C (77, 109.4 and 113 degrees F, 

respectively). Continuous chlorination at a dose of 4 to 6 mg/L resulted in a 5- to 6-log 

decrease of L. pneumophila in six hours. Chlorine disinfection at 43 degrees C (109.4 

degrees F) inactivated L. pneumophila more reliably and completely than disinfection at 

23 degrees C (73.4 degrees F). Due to thermal decomposition of chlorine residual, 

approximately 120 percent more chlorine was needed to maintain a residual of 4–6 mg/L 

at 43 degrees C (109.4 degrees F). The authors noted that in addition to the higher doses 

required to overcome residual decomposition, a drop in chlorine levels or failure of 

chlorination equipment could allow Legionella to survive. As a result, the authors 

concluded that chlorination of hot water systems is more difficult to regulate than that of 

cold water systems. 

• Saby et al. (2005) tested the efficiency of several disinfectants in a hot water system pilot 

unit. The pilot unit was supplied by tap water pre-heated to 30 degrees C (86 degrees F). 

Legionella-contaminated water was mixed with the tap water before heating. 

Colonization of the biofilm by Legionella was found after seven weeks. After 

colonization of pipes in the pilot unit, various treatments were tested. Shock 

hyperchlorination at 50 mg/L of free chlorine residual for 12 hours was found to be very 

effective in reducing Legionella in the water; however, the pipe networks were 

recolonized in three to four weeks. The authors stated this could be explained by the 

inefficiency of shock hyperchlorination treatment on bacteria in biofilms. Continuous 

chlorine at a dose of 3 mg/L for two periods of four weeks was also examined. The 

results showed that this treatment was very effective at maintaining viable bacteria, 

including Legionella, at low levels. However, a malfunction of the chlorination system 

resulted in a positive result for Legionella within 28 hours. The authors concluded that 

continuous chlorination allows only for containment of Legionella and that technical 

problems with treatment could result in rapid recolonization. Temperature control at 40 

degrees C (104 degrees F) and 55 degrees C (131 degrees F) was also evaluated as part of 

this study. While temperature control at 55 degrees C was the best technical and 

economic solution to Legionella control, continuous chlorination was also a good 

solution. 

The interaction of Legionella with co-occurring organisms can affect the efficacy of chlorine in 

the inactivation of Legionella. The following laboratory studies evaluated the effects of cooccurring amoebae on Legionella inactivation by chlorine disinfection: 

• In a study of the interaction of thermotolerant amoebae and Legionella, Storey et al. 

(2004a) evaluated the efficacy of heat and chlorine as disinfectants. The study found that 

a 2-log (99 percent) reduction of free-living (planktonic) L. pneumophila was achieved at 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 17 October 2015 

30 minutes with free chlorine concentrations of 1 mg/L and 2 mg/L (at 37 degrees C, or 

98.6 degrees F). A 3-log (99.9 percent) reduction of L. pneumophila was achieved after 

10 minutes with a free chlorine concentration of 10 mg/L (at 37 degrees C, or 98.6 

degrees F). The efficacy of free chlorine in the reduction of Acanthamoeba castellanii (an 

amoeba)-bound L. erythra was also evaluated. A free chlorine dose of 1 mg/L achieved 

less than 0.5-log reduction at contact times of 60 minutes or less, whereas a 2 mg/L dose 

resulted in a 3-log reduction (99.9 percent) at contact times of >30 minutes (at 37 degrees 

C or 98.6 degrees F). A free chlorine dose of 10 mg/L and contact time of 10 minutes 

achieved a 3.2-log reduction. The study found that the interaction of Legionellae and 

Acanthamoebae increased the resistance of Legionellae to thermal treatment and 

increased their sensitivity to chlorine. The authors also noted the tolerance of

Acanthamoebae to high chlorine doses and thermal treatment. Both cysts retained their 

viability at free chlorine levels of 100 mg/L after 10 minutes and at free chlorine levels of 

less than10 mg/L after 30 minutes. The authors cited a prior study by Kilvington and 

Price (1990) that found that cysts were able to maintain their viability at free chlorine 

concentrations of 50 mg/L or less. 

• Dupuy et al. (2011) also investigated the interaction of amoebae and Legionella. The 

authors compared the efficiency of three oxidizing disinfectants (chlorine, 

monochloramine and chlorine dioxide). These disinfectants were used on three 

Acanthamoeba strains, L. pneumophila alone, and Acanthamoeba and L. pneumophila in 

co-culture. Chlorine efficiency was evaluated at 30 degrees C (86 degrees F) and at 50 

degrees C (122 degrees F). An initial dose between 2 mg/L and 3 mg/L was applied with 

a residual free chlorine residual of 1 mg/L at the end of the treatment. Results were

presented as CT (min-mg/L) values. Chlorine was found to inactivate all three strains of 

Acanthamoeba studied, both infected with L. pneumophila and not infected. At least a 3-

log inactivation (99.9 percent) was obtained for all strains at a CT of approximately 60 

min-mg/L. There was a significant difference in inactivation between the strains of 

Acanthamoeba studied, with more than 3-log inactivation found at a CT of less than 10 

min-mg/L for one strain. Inactivation efficiency was slightly higher at 50 degrees C (122 

degrees F).

The following laboratory studies evaluated the effectiveness of chlorine when biofilm is present: 

• In a 1994 paper, de Beer et al. studied the degree to which chlorine penetrates a biofilm 

based on bulk concentration. For this study, biofilms consisting of Pseudomonas 

aeruginosa and Klebsiella pneumoniae were grown for one week, with a maximal 

thickness of 150–200 micrometers (μm). Transient chlorine concentration profiles were 

measured in biofilms with a microelectrode that was developed for the investigation and 

was sensitive to concentrations of chlorine in the micromolar range. The transient 

chlorine microprofiles showed slow chlorine penetration into the biofilm, with the rate 

dependent on the bulk concentration of chlorine. The penetration time exceeded 60 

minutes even at the highest concentration tested (0.36 millimolar (mM)). The biofilm 

matrix, consisting of cells and extracellular polymeric substances, was determined to be a 

substrate for the chemical reduction of chlorine. Chlorine concentrations measured in 

biofilms were typically only 20 percent or less of the concentration of the bulk liquid. 

The microprofiles showed that following exposure to 2.5 mg/L chlorine for one hour, 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 18 October 2015 

only the upper 100 μm of the cell clusters was penetrated by chlorine. Findings showed 

that the limited penetration of chlorine into the biofilm (as determined by penetration 

depth and rate of penetration) is likely a key factor influencing the reduced efficacy of 

chlorine against biofilms compared to its effectiveness against planktonic cells. Rapid 

regrowth after chlorine treatment may have originated from areas within biofilms that are 

highly resistant to chlorine. 

• Loret et al. (2005) expanded on the de Beer et al. (1994) study by using a simulated 

distribution system consisting of pipe loops to compare disinfectants for Legionella

control in biofilms in building water systems. The pilot unit also included piping off of 

the main pipe loop to simulate areas at the ends of a water system (dead ends) with 

stagnant flow conditions. Tap water and injection of cultured natural Legionella strains 

were used to establish biofilms. Low temperature (35 degrees C, or 95 degrees F) relative 

to hot water systems and low water velocity, as well as high retention times, were 

maintained to favor the growth of Legionella and biofilms. Each pipe loop was treated 

with one of the studied disinfectants for three months. The loop receiving chlorine was 

maintained with a residual dose of 2 mg/L. Each type of disinfectant used in the study 

displayed rapid initial results in the treated loops, with Legionella populations decreasing 

to undetected levels (less than 500 CFU/L, or colony-forming units per liter) within three 

days of treatment, in all cases. However, Legionella remained undetected over the whole 

study period only with sodium hypochlorite, electro-chlorination, chlorine dioxide and 

monochloramine. (Ozone and copper/silver allowed occasional re-emergence of 

detectable Legionella.) Ozone, electro-chlorination and chlorine treatments resulted in a 

reduction of biofilm thickness to below detection limits (<5 μm) after one week. A 

chlorine dosage rate of 2.5 mg/L removed biofilm better than a chlorine dioxide dosage 

rate of 0.5 mg/L. Flushing of the dead ends at a rate of 20 percent of the volume per day 

did not result in a significant reduction in Legionella. After a single complete flushing, all 

so-called dead end sections of piping returned to their initial contamination level within 

24 hours. The study concluded that chlorine and chlorine dioxide were the most effective 

treatment methods in this study (as compared to ozone, monochloramine and 

copper/silver). Ozone was found to be effective for controlling the planktonic and biofilm 

populations within the pipe loops but was ineffective within dead end sections. 

Monochloramine was found to be ineffective for the amoebae and in the biofilm. The 

authors suggest that the experimental protocol did not allow for maintenance of a stable 

product and resulted in insufficient dosing in the pipe loops. 

• Using copper and stainless steel coupons, Cooper and Hanlon (2009) found that mature 

L. pneumophila biofilms (one and two months old) survived a one-hour treatment with 50 

mg/L chlorine and continued to grow after treatment, reaching a population of 106 CFU 

per coupon (20 mm diameter disc). The authors also found that planktonic Legionellae

were able to survive and persist at free chlorine concentrations of 0.5 mg/L. 

Additional studies that compare the effectiveness of other disinfectants to chlorine to control for 

Legionella are cited in subsequent sections for various technologies. 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 19 October 2015 

• In a study of Legionella control in full-scale water systems of older hospital buildings in 

Rome, Italy, Orsi et al. (2014) evaluated the effectiveness of shock hyperchlorination and 

continuous chlorination over a five-year period. Thirty-eight buildings were studied and 

1,308 samples were analyzed for the presence of Legionella. Samples were collected 

before and/or after several chlorination treatment scenarios (before and after shock 

hyperchlorination, shock hyperchlorination followed by continuous chlorination) from 

cold water piping, mixed cold and hot piping, and hot water piping. Shock 

hyperchlorination was described as an applied concentration of 20–50 parts per million 

(ppm), and continuous chlorination was described as a continuously applied 

concentration of 0.5–1.0 ppm. The study found a significant association between the 

presence of Legionella in the building drinking water systems and the lack of continuous 

chlorination following shock hyperchlorination. Isolation of Legionella was more 

frequent in mixed water samples (20–40 degrees C (68–113 degrees F)) than in cold or 

hot water samples. The authors concluded that continuous free chorine levels of 0.5 to 1.0 

mg/L resulted in significant reductions in Legionella counts in the old hospital water 

systems. However, this treatment did not completely eradicate Legionella. 

• Lin et al. (1998a) reported that some hospitals that initially adopted chlorination 

converted to other methods of disinfection because of failure to control Legionella and 

corrosion of the building water system. Also, Casini et al. (2014) isolated Legionella

strains more tolerant of free chlorine from a water system after years of chlorine 

treatment. 

2.3.1.3 Potential Water Quality Issues 

Chlorine can react with organic material in the water to form DBPs in systems with areas of low 

flow or stagnant waters. Some DBPs have been shown to cause cancer and reproductive effects 

in lab animals and may cause bladder cancer and reproductive effects in humans (USEPA, 2010). 

In a simulated distribution system of pipe loops, Loret et al. (2005) found trihalomethane (THM) 

levels >100 micrograms per liter (μg/L), bromate levels >10 μg/L, and chlorite levels >0.2 mg/L 

with an applied chlorine dose of 2 mg/L. Orsi et al. (2014) noted that special equipment was 

needed in certain health care settings (e.g., dialysis, neonatal care) to reduce free chlorine and 

THM levels.

Continuous chlorination at high levels in building water systems can result in objectionable 

tastes and odors along with irritation of skin, eyes and mucous membranes. 

Continuous chlorination can contribute to corrosion, with associated leaks, in plumbing systems 

and may require the simultaneous use of corrosion-inhibiting chemicals. Sarver et al. (2011) 

reported that continuous hyperchlorination increased leaks by up to 30-fold, consistent with 

extensive laboratory work in soft higher-pH waters (Sarver et al., 2011). In a study by 

Grosserode et al. (1993), leaks first appeared in the copper pipes of a water distribution system

about two years after installation of the chlorine injectors. Significant deterioration was noted 

only in the hot water system. The addition of silicate corrosion inhibitors reduced the total 

number of leaks per year by >80 percent.
Draft – Technologies for Legionella Control: 

Scientific Literature Review 20 October 2015 

2.3.1.4 Operational Conditions 

Parameter Conditions Indicating Operational Effectiveness

The efficacy of chlorination is affected by many factors, including chlorine concentration, 

contact time, pH, temperature, buffering capacity of the water, concentration of organic matter, 

and the number and types of microorganisms in the water system (in biofilms and free-living). 

Sidari et al. (2014) reported that the typical concentration of supplemental chlorine is 2–4 mg/L 

as free residual chlorine. Lin et al. (2002) reported that 2–6 mg/L of chlorine was needed for 

continuous control of Legionella in water systems. The bactericidal action of the chlorine is 

enhanced at higher temperatures and at lower pH levels. The anti-microbial efficacy of chlorine 

declines as pH increases >7, with significant loss of efficacy at pH >8. However, free chlorine is 

degraded rapidly at elevated water temperatures, which is a concern for hot water chlorination 

(Health Protection Surveillance Centre, 2009). 

Operational Considerations 

To help ensure its effectiveness, standard industry practices recommend how sodium 

hypochlorite should be stored and handled to minimize decomposition of the product 

(GLUMRBSPPHEM 2012). It should be stored in the original shipping containers or compatible 

containers and sited away from direct sunlight in a cool area. Feed rates should be regularly 

adjusted to account for any losses in chlorine content during storage or handling. 

NSF/ANSI Standard 60 certification can help ensure that the quality and effectiveness of water 

treatment chemicals have been reviewed and found to be acceptable for potable water 

applications. A facility considering application of chlorine gas as the form of chlorine to be used 

for disinfection would also need to consider potential safety and security concerns. The Chemical 

Facility Anti-Terrorism Standards include information on standard practices for storage and 

handling of chlorine gas (Department of Homeland Security, 2015). Additional safety procedures 

will likely be required for personnel training and equipment. Existing OSHA, state or local fire 

authority regulations may apply and may need to be consulted.

Monitoring Frequency and Location 

The Surface Water Treatment Rule (SWTR) (USEPA, 1989a) requires that all PWSs using 

chlorine and using surface water or ground water under the direct influence of surface water 

monitor for the presence of the residual disinfectant in the distribution system or at the point-ofentry (POE) to the distribution system. The disinfectant level must be >0.2 mg/L at the POE and 

detectable within the distribution system. 

The Stage 1 Disinfectants and Disinfection Byproducts Rule (Stage 1 DBPR) requires PWSs that 

use chlorine to maintain a maximum residual disinfectant level (MRDL) as running annual 

average less than 4.0 mg/L (USEPA, 1998). 

As stated in the SWTR, PWSs that use chlorine are required to monitor for combined or total 

chlorine residual or heterotrophic plate count (HPC) bacteria in the distribution system at 

locations that have been approved by the primacy agency. All these parameters could provide 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 21 October 2015 

operational information to indicate the need for chlorine dose adjustments, system flushing and 

managing water age within finished water storage facilities.

Maintenance Needs 

Operating and maintenance practices for chlorine disinfection systems include maintenance of an 

appropriate disinfectant residual, regular system cleaning and flushing, inspections, and water 

quality monitoring. Newly constructed or rehabilitated piping systems are cleaned and flushed 

prior to initial disinfection. Routine flushing and water quality monitoring are recommended to 

assure that adequate disinfectant levels are maintained throughout the building water system 

(HSE, 2014; Rosenblatt and McCoy, 2014). 

Since chlorine is recognized as being less effective than other disinfectants at penetrating and 

controlling established biofilms, chlorination may not be effective if large amounts of scale and 

sediment are present in the system. These solids are prone to biofilm formation and may need to 

be removed by cleaning before effective disinfection can be achieved (HSE, 2014). Loret et al. 

(2005) recommended flushing dead ends daily with disinfected water and removing building 

finished water fixtures and pipes that are rarely used. 

2.3.2 Monochloramine

2.3.2.1 Background 

The primary use of monochloramine (NH2Cl) in water systems is for residual disinfection to 

maintain a disinfectant residual in the distribution system. Monochloramine has a more persistent 

and stable disinfectant residual than chlorine (USEPA, 1994). It causes fewer unpleasant tastes 

and odors in drinking water than other disinfectants (USEPA, 1994). Monochloramine has a 

much lower disinfection efficacy than free chlorine (Symons, 1978) and if used as a primary 

disinfectant it requires a much longer contact time. Often ammonia is added after chlorine has 

acted as a primary disinfectant for a period of time, and the resulting monochloramine is used as 

a residual disinfectant (USEPA, 1999b; USEPA, 1999c). 

Monochloramine is effective for controlling bacterial regrowth and controlling biofilms due to its 

ability to penetrate the biofilm, although excess ammonia can cause biofilm growth (USEPA, 

1999c; LeChevallier et al., 1988a). Monochloramine and chlorine have different mechanisms of 

action; monochloramine is more specific, and chlorine reacts with a wider array of compounds. 

When inactivating bacteria in the biofilm, monochloramine is able to penetrate, whereas chlorine 

may get consumed through reactions that do not occur with monochloramine (Lee et al., 2011; 

LeChevallier, 1988b). For equivalent chlorine concentrations, monochloramine was shown to 

initially penetrate biofilm 170 times faster than free chlorine, and even after subsequent 

application to a monochloramine-penetrated biofilm, free chlorine penetration was limited (Lee 

et al., 2011). The mechanism of inactivation for chloramine is thought to involve inhibition of 

proteins or protein-mediated processes such as respiration (USEPA, 1999c). 

Monochloramine can be formed by first adding chlorine then ammonia or vice versa. Although 

monochloramine is the dominant form produced under conditions typically found in a drinking 

water system, two other forms of chloramines (dichloramine and trichloramine (nitrogen 

trichloride)) can also be produced when excessive levels of hypochlorite are present or at low pH 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 22 October 2015 

levels (USEPA, 1994). Monochloramine is the preferred form of chloramine for use in drinking 

water treatment due to fewer taste and odor issues and its disinfection efficacy. Monochloramine 

is a colorless water-soluble liquid (Kirk-Othmer, 1979) with a freezing point at -66 degrees C (-

86.8 degrees F). 

Monochloramine has been used in the treatment of drinking water for nearly 100 years (USEPA, 

2009). It was first used in water treatment in the mid-1910s; the City of Ottawa first used 

chloramines in 1915 due to the rising costs of bleach. Denver, Colorado, started using 

monochloramine around the same time as a way to control organisms in the distribution system 

(Symons, 1978). Its use gained popularity in the 1930s and 1940s but soon declined due to the 

shortage of ammonia during World War II. The use of monochloramine has been increasing in 

the past couple of decades due to concerns over DBPs associated with chlorine use (USEPA, 

1999c). As of 2009, 1 in 5 Americans were using drinking water treated with chloramines 

(USEPA, 2009) and this usage rate is projected to increase due to implementation of the Stage 2 

DBPR (Seidel et al., 2005; USEPA, 2005a). 

2.3.2.2 Characterization of Effectiveness against Legionella

Laboratory studies have used a wide range of CT values under different water quality test 

conditions for inactivating Legionella. 

• Jakubek et al. (2013) evaluated inactivation of L. pneumophila in nuclear power plant 

cooling circuits with monochloramine formed by combining sodium hypochlorite and 

ammonia solution with a chlorine-to-ammonia mass ratio of 4.8 (at pH 7.5–8.5 and 25–35 

degrees C (or 77–95 degrees F)). The results showed 99.9 percent (3-log) inactivation of 

L. pneumophila with a CT range between 16.14±3.07 min-mg/L and 64.88±19.07 minmg/L. The study also found that temperature, pH and initial bacterial concentration 

affected the ability of monochloramine to inactivate Legionella. Increasing the 

temperature had a positive effect on monochloramine activity but a negative effect on the 

contact time required to inactivate 99.9 percent of the Legionella. Increasing the pH had a 

negative effect on monochloramine activity but a positive effect on the contact time 

required to inactivate 99.9 percent of the Legionella (Jakubek et al., 2013). 

• Jacangelo et al. (2002) examined inactivation of waterborne emerging pathogens such as

Legionella by selected disinfectants, including monochloramine. Pre-formed 

monochloramine was used at a target pH of 7.0. Two different temperatures (5 degrees C 

(41 degrees F) and 25 degrees C (77 degrees F)) and two different mass ratios of chlorine 

to ammonia (3:1 and 7:1) were examined. The observed CT values for 99 percent 

inactivation (2-log reduction) of L. pneumophila ranged from >320 to >1,000 min-mg/L. 

At a water temperature of 5 degrees C (41 degrees F), the CT value at a 3:1 ratio was 

>1,000 min-mg/L and was >320 to >1,000 min-mg/L at a 7:1 ratio. At a temperature of 

25 degrees C (77 degrees F), the CT was >630 to >1,000 min-mg/L at a 3:1 ratio and was 

>320 to >1,000 min-mg/L at a 7:1 ratio. These CT values were similar to CT values for 

Giardia inactivation under the same conditions (Jacangelo et al., 2002). 

• Donlan et al. (2002) conducted a study with three different monochloramine 

concentrations (0.2 mg/L, 0.5 mg/L and 1.5 mg/L) and three different contact periods (15, 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 23 October 2015 

60 and 180 minutes). All scenarios involved a temperature of 30 degrees C (86 degrees F) 

and a pH of 7. A monochloramine concentration of 0.2 mg/L was ineffective for all 

contact periods. At the 0.5 mg/L concentration and 180 minute contact time, 99 percent 

of Legionella was inactivated (i.e., 2-log removal). Using the 1.5 mg/L concentration of 

monochloramine, 99.9 percent of Legionella was inactivated (i.e., 3-log removal) at 60 

and 180 minutes contact time (Donlan et al., 2002). 

• A study conducted by Cunliffe (1990) evaluated Legionella contact time in a lab 

simulated model experiment. This study used a 2.5:1 chlorine-to-ammonia mass ratio 

prepared by mixing ammonium chloride with sodium hypochlorite at 30 degrees C (86 

degrees F) and pH 8.4–8.6. The average CT level for 99 percent inactivation was 15 minmg/L. The results showed that Legionella was more sensitive to monochloramine than E. 

coli (Cunliffe, 1990). 

The wide range of CT values reported in the literature could be due to different water quality 

conditions and different methodologies used for inactivating Legionella. 

Several studies reported on the efficacy of monochloramine in controlling Legionella when 

biofilm is present on pipe surfaces. 

• Wang et al. (2012) evaluated the effects of disinfectant (chlorine and chloramine), water 

age (1 to 5.7 days), and pipe material (polyvinyl chloride, iron and cement) on multiple 

pathogens, including Legionella, using simulated distribution systems. Two sampling 

events occurred after six and 14 months. The results showed systems treated with 

chloramines had higher levels of bacteria and protozoa at shorter water ages than systems 

treated with chlorine. Chloramine concentrations were depleted faster than chlorine due 

to nitrification of the chloramine. The effects of pipe type on pathogen growth mainly 

became evident after water age reached 5.7 days, after the majority of the disinfectant 

residual was depleted. Legionella was only detected during the 14-month sampling event 

in bulk water and at lower water ages for chloraminated systems. 

• Dupuy et al. (2011) evaluated the inactivation of both free and intracellular L. 

pneumophila (co-occurring with Acanthamoeba) using different disinfectants. The results 

showed no difference between the inactivation of both forms of Legionella by 

monochloramine, while the other disinfectants (chlorine and chlorine dioxide) were not 

as efficient in inactivating the intracellular Legionella. 

• Loret et al. (2005) evaluated disinfectants and their effects on biofilm. They studied 

Legionella control in a pipe loop receiving continuously treated water. Monochloramine 

treatment was evaluated for one month. The ratio of chlorine to ammonia for 

monochloramine was 2:1, and an average dose of 0.5 mg/L was used. Planktonic 

Legionella decreased to undetectable levels after three days and stayed undetectable for 

the remainder of the month. There were no viable Legionella in the biofilm after six days 

of treatment. Biofilm thickness increased with monochloramine treatment after one 

month of treatment, unlike with the other disinfectants (e.g., chlorine, chlorine dioxide). 

The study results showed that monochloramine was effective against Legionella, but it 

was not effective in removing the biofilm completely (Loret et al., 2005). 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 24 October 2015 

• Türetgen (2004) conducted a study of the efficacy of monochloramine and chlorine 

against biofilms using different contact times and different concentrations on a full-scale 

and model system cooling tower. Monochloramine was found to be significantly more 

effective against cooling tower biofilms than free chlorine. In both systems, a 3-log (99.9 

percent) reduction of heterotrophic biofilm bacteria was achieved using a 

monochloramine concentration of 1.5 ppm for a contact time of about 35 minutes. 

Monochloramine is unaffected by the elevated pH levels within the cooling towers, 

unlike chlorine. To completely remove biofilms from a cooling tower additional 

treatment would be needed, such as physical cleaning (Türetgen, 2004). 

• Lee et al. (2011) and Pressman et al. (2012) used microelectrodes to investigate the 

penetration of chlorine, monochloramine, oxygen and free ammonia in nitrifying biofilm. 

While this research clearly demonstrated that monochloramine had a greater penetration, 

the authors found this penetration did not necessarily translate to immediate viability loss. 

Even though free chlorine’s penetration was limited compared to that of 

monochloramine, it more effectively (on a cell membrane integrity basis) inactivated 

microorganisms near the biofilm surface. The authors also found that the presence of 

higher free ammonia concentrations allowed a larger biomass to remain active during 

monochloramine application, particularly the organisms deeper within the biofilm, 

leading to faster recovery in oxygen utilization when monochloramine was removed. The 

authors suggested that limiting the free ammonia concentration during monochloramine 

application would slow the onset of nitrification episodes by maintaining the biofilm 

biomass at a state of lower activity.

• Donlan et al. (2002) evaluated Legionella levels within a biofilm reactor. They found 

monochloramine to be more effective than chlorine in identical conditions for Legionella 

inactivation, leading the authors to conclude that monochloramine may be more effective 

for the inactivation of Legionella in drinking water distribution systems. 

Several studies evaluated Legionella control in building water systems receiving water from a 

distribution system where the treatment plant converted from chlorine to monochloramine. 

Several studies evaluated the addition of monochloramine for the treatment of building water 

systems. Other studies compared Legionella control in water systems using different disinfection 

methods. 

• Baron et al. (2014) studied the microbial ecology of a hot water system within a hospital 

following the introduction of monochloramine. Samples were taken three months before 

and immediately prior to the addition of an on-site monochloramine generation system 

and then every month for six months after the addition. Monochloramine levels were 

targeted at 1.5–3.0 mg/L as chlorine. Samples were taken at multiple sites within the 

hospital’s hot water system and analyzed by three methods. The authors observed a shift 

in microbial ecology immediately after the addition of the disinfectant, and the number of 

operational taxonomic units significantly increased. Microbial ecology variation based on 

sampling location within the hospital’s hot water system (including automatic and 

standard faucets) increased after the addition of monochloramine. There was a 

statistically significant increase in the relative abundance of genera associated with 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 25 October 2015 

denitrification after the addition of monochloramine. Waterborne pathogen-containing 

genera were also examined. After the addition of monochloramine, an increase in counts 

of Acinetobacter, Mycobacterium, Pseudomonas and Sphingomonas were observed. 

Trends for Legionella counts varied but did not show an increase. The addition of 

monochloramine to the hospital’s water system had an impact on the types and amounts 

of microorganisms found in the hot water system. 

• Whiley et al. (2014) measured Legionella spp., L. pneumophila and mycobacterium 

avium complex in two drinking water distribution systems: DS1, using chlorine 

disinfection, and DS2, using chloramine disinfection. Samples were collected and 

disinfectant residual was measured four times throughout the year and at different 

distances. In DS1, the five sampling sites were located between 5 and 22 kilometers (km) 

from the treatment plant and had free chlorine residuals in the range of 0.2 to 1.3 mg/L. 

In DS2, the five sampling sites were located between 1 and 137 km from the treatment 

plant and had monochloramine residuals in the range of <0.05 (at a dead-end location) to 

3.9 mg/L. All three microbes were detected throughout the distribution system and at 

different points throughout the year. The only recurring trend was an increase in 

microorganisms when the disinfectant residual decreased (for both chlorine and 

chloramine), especially at dead ends in the system (<0.05 mg/L of monochloramine). 

• Duda et al. (2014) observed a significant reduction in Legionella at distal sites after a 

monochloramine generation system was installed in a hospital hot water system. The 

observations were based on 29 months of monitoring data including a five-month 

baseline period and 24 months’ data following installation.

• A hospital in Italy added monochloramine treatment into a hot water network within the 

building using a device to continuously distribute monochloramine (Marchesi et al., 

2013; Marchesi et al., 2012). The disinfectant levels were maintained between 1.5 and 3.0 

mg/L. Hot water samples were analyzed for Legionella spp. and Pseudomonas spp. over 

a one-year period. Both organisms decreased in terms of the number of positive samples. 

Before the addition of continuous treatment, 97 percent of samples were positive for 

Legionella. After treatment, 13.3 percent of samples were positive for Legionella. The 

authors concluded that based on this full-scale study, continuous injection of 

monochloramine in a building hot water system has potential for controlling Legionella 

(Marchesi et al., 2012). Marchesi et al. (2013) continued the study for a total of 36 

experimental months with the same parameters for monochloramine and confirmed that 

Legionella control with monochloramine was rapid, as 7 out of the 8 positive samples 

occurred within the first eight months of the total 36-month experimental period. The 

eighth positive sample occurred at 15 months, when the monochloramine dosage rate 

decreased below 1 mg/L. Use of monochloramine did not increase chlorite levels and 

nitrification did not occur. The authors suggested that a monochloramine concentration 

between 2 and 3 mg/L should be maintained to assure a Legionella concentration below 

102 CFU/L.

• Weintraub et al. (2008) evaluated water and biofilm samples from 53 buildings in San 

Francisco before and after conversion to monochloramine for residual disinfection in 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 26 October 2015 

February 2004. Chlorine was used for primary disinfection throughout the study period. 

The total chlorine level in finished water was 0.6 mg/L on average prior to conversion 

and 1.97 mg/L on average in 2004 following conversion. Samples were collected from 

each building six times during the two-year study period—three samples before and after 

the conversion to monochloramine. Sampling results showed that 60 percent of hot water 

systems and 72 percent of buildings contained Legionella before conversion to 

monochloramine compared to 4 percent of hot water systems and 9 percent of buildings 

after the conversion. After the conversion to monochloramine, there was an approximate 

10-fold increase in the concentration of total chlorine in the buildings’ hot water systems. 

Also, prevalence of Legionella decreased by 96 percent in POU outlets when controlling 

for building and water characteristics (Weintraub et al., 2008). 

• Flannery et al. (2006) compared Legionella colonization of hot water systems for two 

years to determine if a conversion from chlorine to monochloramine in the drinking water 

system would reduce Legionella levels in the building hot water system. The results 

showed 60 percent colonization of the hot water system before conversion and 4 percent 

colonization after the conversion. After switching to a disinfectant with a more stable 

residual, higher concentrations of total chlorine were measured within building hot water 

systems. The authors concluded that increasing the amount of water supplies disinfecting 

with monochloramine might reduce the incidence of Legionnaires’ disease. 

• Moore et al. (2006) evaluated Legionella colonization within building water systems after 

the wholesale PWS had converted from chlorine to monochloramine for residual 

disinfection treatment. Legionella colonization of building water systems decreased from 

19.8 percent (19 of 96 buildings) to 6.2 percent (6 of 96 buildings). The samples in this 

study were taken a few months before and a few months after the conversion to 

monochloramine (Moore et al., 2006). 

• Heffelfinger et al. (2003) concluded that hospital water systems using a monochloramine 

disinfectant residual were at a lower risk of Legionnaires’ disease cases than systems 

using a chlorine residual, based on survey data. Out of 459 surveys sent, 166 hospitals 

responded (36 percent response rate). Of the 166 survey respondents, 38 (25 percent of 

survey respondents) were selected as case studies because they had reported definite 

cases of Legionnaires’ disease in the period 1994 to 1998 or outbreaks of hospitalacquired Legionnaires’ disease in the period 1989 to 1998, and they had not changed 

their water disinfection practices during the study period. Six of the 38 case study 

hospitals (16 percent) used monochloramine for disinfection of the municipal water 

supply. Of the 128 survey respondents that reported no cases of Legionnaires’ disease 

during the study period, 59 (46 percent) used monochloramine disinfection. The hospitals 

supplied by drinking water with a monochloramine disinfectant residual were less likely 

to have definite cases or outbreaks than hospitals with chlorine disinfectant residuals 

(adjusted odds ratio: 0.20; confidence interval (95 percent): 0.07–0.56). 

• Kool et al. (2000) conducted a case control study comparing disinfection methods in 

water supplied to hospitals with reported Legionnaires’ disease (32 hospitals) with the 

disinfection methods used in water supplied to control hospitals (48 hospitals) with no 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 27 October 2015 

reported disease. They found that hospital water systems supplied with water treated by 

chlorine were more likely to have reported an outbreak of Legionnaires’ disease than 

hospitals supplied with water treated by monochloramine (odds ratio 10:2 and 95 percent 

confidence interval: 1.4–460). The authors infer that 90 percent of the outbreaks might

have been prevented had the residual used in the case hospitals contained 

monochloramine (Kool et al., 2000; Kool et al., 1999). The cases in this study were based 

on previous records of infections and not on Legionella measurements in the water 

supply (Kim at al., 2002; Lin et al., 2000a).

2.3.2.3 Potential Water Quality Issues 

Potential water quality issues with monochloramine include corrosion, formation of DBPs, and 

nitrification. Monochloramine can impact kidney dialysis and should be removed from the 

dialysate water. Monochloramine should be removed from water used for fish tanks due to 

detrimental effects.

An unintended consequence of using monochloramine is corrosion of the pipes and materials 

used in water systems. Corrosion can occur in two forms, including pitting and a more uniform 

thinning of pipe surfaces. Kirmeyer et al. (2004) reported that chloramine can attack rubber and 

plastic components in a water system and that 23 percent of utilities surveyed experienced an 

increase in degradation of rubber materials after chloramine disinfection was implemented. 

Water temperature, pH and disinfectant concentration also affect corrosion rates. 

Monochloramine can react with pipe scale differently than other disinfectants, resulting in lead 

leaching in system materials containing lead (Edwards and Dudi, 2004). Corrosion control and 

maintenance of building water systems will be important to consider before adding disinfectants. 

Further research is needed to evaluate the interactions of disinfectants with water chemistry and 

piping materials in a building water system and to better understand the effects of these 

interactions on the efficacy of pathogen inactivation (Rhoads et al., 2014). 

Another unintended consequence of monochloramine disinfection is its ability to react with 

organics in the water to form DBPs. Although chloramination significantly reduces some DBPs, 

such as THM and haloacetic acids (HAA), its usage can contribute to the formation of other 

DBPs such as nitrosamines. For more information regarding nitrosamines please see the Nnitrosodimethylamine (NDMA) fact sheet (USEPA, 2014b) on EPA’s website. 

Nitrification is a potential problem for utilities that utilize chloramines as a disinfectant and may 

occur when finished water contains excess ammonia and low chloramine residual (Kirmeyer et 

al., 2004). Areas of the distribution system with higher water age and warmer temperatures are 

more susceptible to nitrification. Nitrification is a microbiological process that oxidizes ammonia 

to form nitrite and nitrate. Increased nitrate levels provide nutrients for the growth of nitrifying 

bacteria. Nitrification can also degrade the aesthetic quality of the water resulting in taste and 

odor issues as well as particles in the water (AWWA, 2013). Breakpoint chlorination can occur 

due to imbalances in chlorine and ammonia concentrations, resulting in the formation of nitrate, 

nitrogen chloride and nitrogen gas. Once nitrification occurs, maintaining monochloramine 

disinfectant residual becomes very difficult within the nitrified areas of the distribution system, 

allowing pathogenic organisms that may be present in biofilm or pipe scale to proliferate. The 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 28 October 2015 

American Water Works Association’s (AWWA) Manual M56 recommends that any utility using 

chloramines develop and implement a nitrification control plan (AWWA, 2013). 

Monochloramine can inhibit biological growth on filters, which could be positive in that it helps 

keep the filters clean, but this inhibition can also reduce biodegradable dissolved organic carbon 

removal, a problem if the filters were put in place for that purpose. 

Converting disinfection to monochloramine can have an impact on organisms other than 

Legionella. A study by Moore et al. (2006) found that, in addition to Legionella, building water 

systems were colonized with mycobacteria before and after a conversion from chlorine to 

monochloramine in the PWS. The proportion of buildings colonized with mycobacteria increased 

from 19.1 percent during the chlorine phase to 42.2 percent after the conversion to 

monochloramine. The number of samples within the distribution system containing detectable 

levels of coliform increased from two samples during the chlorine phase to twenty samples after 

the conversion (Moore et al., 2006). 

Pryor et al. (2004) saw similar results in a study conducted in Florida. After conversion to 

monochloramine, mycobacteria increased, total coliforms and heterotrophic bacteria levels 

increased, and nitrification occurred in the storage tanks (Pryor et al., 2004). Building water 

system operators who consider treating water with monochloramine to control for Legionella 

should be cognizant of potential unintended consequences such as increases in mycobacteria and 

other waterborne pathogens and take the necessary protective measures to protect public health. 

2.3.2.4 Operational Conditions 

Parameter Conditions Indicating Operational Effectiveness 

The normal dosage rate for monochloramine is between 1.0 and 4.0 mg/L. 

The case studies cited above generally support maintaining a chloramine residual in the building 

water system in the range of 1 to 2 mg/L as an effective means for containing biofilm growth, 

minimizing Legionella colonization, and preventing outbreaks. As such, building water system 

maintenance such as appropriate pH, chlorine-to-ammonia ratios, flushing, and frequent 

monitoring to demonstrate residual maintenance on an ongoing basis are essential. The current 

practice is to use a chlorine-to-ammonia ratio of 3:1 to 5:1 to produce monochloramine. The 

amount of organic nitrogen in the water prior to addition of ammonia will also affect how much 

ammonia is needed to reach the desired ratio (USEPA, 1999c). 

The rate of reaction for the conversion of chlorine to monochloramine is sensitive to pH and can 

also be affected by contact time and temperature. The optimum pH range for formation of 

monochloramine is 7.5 to 9 (WHO, 2004). Monochloramine is relatively stable under varying 

temperatures once formed. Cunliffe (1990) evaluated monochloramine decay at two different 

temperatures. Water incubated at 55 degrees C (131 degrees F) showed a loss of residual after 50 

hours, from 1.3 to 0.35 mg/L. After 5 days at 30 degrees C (86 degrees F), the concentration 

dropped from 1.3 to 0.8 mg/L. 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 29 October 2015 

Installation Considerations 

Guidelines for design and implementation of chloramination systems include the following: 

• AWWA M56 Manual, Nitrification Prevention and Control in Drinking Water. Second 

Edition. (AWWA, 2013). 

• Simultaneous Compliance Guidance Manual for the Long Term 2 and Stage 2 DBP Rules 

(USEPA, 2007). 

• The Water Research Foundation manual Optimizing Chloramine Treatment (Kirmeyer et 

al., 2004). 

• Alternative Disinfectants and Oxidants Guidance Manual (EPA 815-R-99-014) (USEPA, 

1999c).

Monitoring Frequency and Location 

The SWTR (USEPA, 1989a) requires that all PWSs using monochloramine and using surface 

water or ground water under the direct influence of surface water monitor for the presence of a 

disinfectant residual in the distribution system and at the POE to the distribution system. The 

disinfectant level must be at least 0.2 mg/L at POE and detectable in at least 95 percent of 

samples collected within the distribution system. 

Stage 1 DBPR also requires PWSs that use monochloramine to maintain an MRDL running 

annual average of less than 4.0 mg/L (USEPA, 1998). 

PWSs that use chloramines are required to monitor for combined or total chlorine residual or 

HPC in the distribution system at locations that have been approved by the primacy agency. All 

of these parameters could provide operational information to indicate the need for chloramine 

dose adjustments, system flushing and water age management within finished water storage 

facilities.

Monochloramine can be measured by amperometric titration (Symons, 1978), N,N-diethyl-pphenylenediamine (DPD) ferrous titrimetric, DPD colorimetric methods (USEPA, 1999c), and 

commercially available adapted indophenol methods (Hach MonochlorF) (Lee et al., 2007). The 

EPA has approved multiple methods for measuring combined chlorine as well as total chlorine. 

A list of approved methods is available through EPA’s website (USEPA, 2014a).

Other monitoring should be conducted to identify the onset of nitrification, which is common in 

systems that use chloramination. Kirmeyer et al. (2004) recommended monitoring HPC, 

chloramine residual, ammonia, nitrate and nitrite to detect nitrification in the distribution system. 

A system-specific monitoring plan should be developed to identify sampling locations, 

parameters and sampling frequency. 

Maintenance Needs 

Operating and maintenance practices for chloramine disinfection systems include maintenance of 

an appropriate disinfectant residual, regular system cleaning and flushing, inspections, and water 

quality monitoring. Newly constructed or rehabilitated piping systems are cleaned and flushed 

prior to initial disinfection. Routine flushing and water quality monitoring are recommended to 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 30 October 2015 

assure that adequate disinfectant levels are maintained throughout the building water system

(HSE, 2014; Rosenblatt and McCoy, 2014). 

Systems using monochloramine as a residual disinfectant periodically use free chlorine to 

eliminate biological growth that may have occurred in the distribution system or on equipment 

(AWWA, 2013; Lin et al., 2000b).

Approaches for preventing nitrite and nitrate formation within the distribution system include 

decreasing water age through flushing or operational changes, increasing the pH, decreasing 

temperature, decreasing total organic carbon concentration, increasing monochloramine 

residuals, increasing the chlorine-to-ammonia ratio, and decreasing the excess ammonia 

concentration (USEPA, 1999c). 

2.3.3 Chlorine Dioxide

Chlorine dioxide is a water-soluble gas that can easily diffuse through cell membranes of 

microorganisms. It has been found to be superior in penetrating biofilms as compared to chlorine 

(Lin et al., 2011b). It is a very effective disinfectant (when used correctly) at inactivating 

bacterial, viral and protozoan pathogens and has a high oxidation potential (USEPA, 1999b). Its 

use as a biocide can be maintained over a wider pH range than chlorine or CSI (Lin et al., 

2011b). 

Chlorine dioxide was first used as a disinfectant in the early 1900s at a spa in Belgium, and its 

use in drinking water disinfection became more common in the 1950s (USEPA, 1999b). In the 

1970s, more than 100 U.S. water treatment facilities used chlorine dioxide for taste and odor 

control, iron and manganese oxidation, or final disinfection, while in Europe, it was being used 

at several thousand water treatment facilities, primarily for final disinfection (Symons et al., 

1977). In the 1980s, use of chlorine dioxide as an alternative primary disinfectant to chlorine 

increased in the United States after EPA promulgated a regulation for total trihalomethanes 

(TTHMs) (Aieta and Berg, 1986). Since the late 1980s, chlorine dioxide has been evaluated 

(Dupuy et al., 2011; Loret et al., 2005; Jacangelo et al., 2002; Berg et al., 1988) and later 

implemented as an effective disinfectant to control Legionella and biofilm in hot and cold 

building water systems (Casini et al., 2014; Marchesi et al., 2013; Cristino et al., 2012; Marchesi 

et al., 2011; Zhang et al., 2009; Sidari et al., 2004).

Use of chlorine dioxide in PWSs is regulated by the DBPR. Chlorine dioxide itself can cause 

acute health effects and has an MRDL of 0.8 mg/L. Chlorite, a DBP of chlorine dioxide 

disinfection, is also regulated by EPA due to potential health concerns. The Stage 1 DBPR sets a 

maximum contaminant level (MCL) of 1.0 mg/L for chlorite. 

2.3.3.1 Characterization of Effectiveness against Legionella

Chlorine dioxide is usually generated on site from sodium chlorite solutions and one or more 

other chemical precursors (e.g., sodium hypochlorite, hydrochloric acid, sulfuric acid) or by an 

electrochemical oxidation process. Stock solutions produced on-site typically have a 

concentration of 500 mg/L. Chlorine dioxide gas cannot be compressed or stored commercially 

because it is explosive under pressure. Therefore, it is never shipped (USEPA, 1999b). Water 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 31 October 2015 

treatment chemicals must meet the appropriate ANSI/AWWA standards or NSF/ANSI Standard 

60 (GLUMRBSPPHEM 2012). 

Laboratory and pilot-scale testing have generally shown that chlorine dioxide disinfection can be 

effective in controlling Legionella: 

• Dupuy et al. (2011) compared chlorine dioxide, chlorine and monochloramine in treating 

L. pneumophila and Acanthamoeba strains alone or in co-cultures (i.e., L. pneumophila

grown within amoebae). Dosage rates were 0.4 mg/L for chlorine dioxide, 2–3 mg/L for 

chlorine (for a residual free chlorine concentration of ~1 mg/L), and 0.8 mg/L for 

monochloramine. All samples were treated with disinfectant for one hour and then the 

disinfectant residual was measured. Chlorine and chlorine dioxide were more efficient at 

reducing (i.e., providing at least a 3-log (99.9 percent) reduction of the bacterial 

population at study conditions) free L. pneumophila than co-cultured L. pneumophila. 

Chlorine dioxide was found to be highly efficient in inactivation of Acanthamoeba M3 

amoebae only, less so in inactivating the other two Acanthamoeba strains discussed in the 

paper. 

• Loret et al. (2005) compared the performance of several alternative disinfectants under a 

controlled pilot-scale simulation of a typical building water system. Tap water and 

injection of cultured natural Legionella strains were used to establish biofilms in each 

pipe loop. Low temperature (35 degrees C, or 95 degrees F) and low water velocity were 

maintained to favor the growth of Legionella and biofilms. Each pipe loop was treated 

with one of the studied disinfectants for three months. The target dosage rate for chlorine 

dioxide was 0.5 mg/L. The authors determined that chlorine dioxide and chlorine were 

the most effective in controlling Legionella, biofilm and protozoa. Chlorine dioxide had 

longer residual activity in the system than did chlorine. Chlorite levels were measured in 

the chlorine dioxide pipe loop at levels >0.2 mg/L. Legionella populations decreased to 

undetected levels (<500 CFU/L) within the first three days of treatment for all 

disinfectants. Biofilm reduction started one week after treatment was initiated, and 

biofilm thickness was reduced to <5 μm with chlorine dioxide and several other 

disinfectants, as compared to a measured biofilm thickness of 13–35 μm in the untreated 

pipe loop. 

• Jacangelo et al. (2002) conducted laboratory studies to evaluate chlorine dioxide, free 

chlorine and monochloramine for inactivation of waterborne emerging pathogens, 

including Legionella. The chlorine dioxide dose rate was 1.0 mg/L. Two different 

temperatures (5 and 25 degrees C, or 41 and 77 degrees F) and two different pH values 

(6.0 and 8.0) were examined. The observed CT values for 2-log reduction of Legionella 

were reported. At 5 degrees C, the observed CT values ranged from >320 to >1,000 minmg/L at pH 6.0 and from >250 to 630 min-mg/L at pH 8.0. At 25 degrees C, the observed 

CT values ranged from 50 to 200 at pH 6.0 min-mg/L and from 50 to 130 min-mg/L at 

pH 8.0. 

Chlorine dioxide disinfection systems have been installed in many hospitals to control Legionella

and biofilm in hot and cold water systems (Casini et al., 2014; Marchesi et al., 2013; Cristino et 

al., 2012; Marchesi et al., 2011; Zhang et al., 2009; Sidari et al., 2004). 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 32 October 2015 

• Casini et al. (2014) reported the application of a WSP approach using multiple 

disinfectants and filtration to control Legionella in a hospital’s hot water system. The 

multi-barrier strategy was developed and refined over a 9-year period. Continuous 

disinfection with chlorine dioxide (0.4–0.6 mg/L in recirculation loops) was provided. 

Additional treatment included endpoint filtration and a shift to monochloramine 

disinfection (2–3 mg/L) after chlorine-tolerant Legionella spp. were identified. After nine 

years, the number of sampling sites that were positive for Legionella decreased by 51 

percent, from 66.7 percent to 32.9 percent, and the mean Legionella count decreased by 

78 percent. 

• Marchesi et al. (2013) reported a strong reduction in Legionella contamination in three 

hospital hot water systems over a three-year period compared to the untreated systems. A 

dosage rate of 0.50–0.70 mg/L chlorine dioxide was applied to the hot water systems, 

with the goal of maintaining a minimum concentration of 0.30 mg/L at distal sites (i.e., 

sink taps, tubs and showers located at distant points in the building water system. On 

average, the three systems reduced Legionella occurrence from 96 percent of sampling 

sites to 46 percent. 

• Cristino et al. (2012) described use of chlorine dioxide for chemical shock treatment and 

continuous treatment after the hot water system in a long-term care facility was found to 

be colonized with L. pneumophila. In addition to thermal shock and chemical shock with 

peracetic acid, chlorine dioxide was applied at a dose sufficient to obtain a 5-mg/L 

residual throughout the building water systems for a one-hour contact time. The water 

was then drained and fresh water introduced to the systems until the chlorine dioxide 

residual was <0.3 mg/L. A continuous chlorine dioxide system was installed in the hot 

water supply at a dose sufficient to maintain a minimum 0.3-mg/L residual at distal taps. 

The shock treatment reduced Legionella counts from 104

–105 CFU/L to zero to 102

CFU/L. Environmental monitoring conducted during the continuous chlorine dioxide 

treatment period showed that Legionella counts remained at stable levels (zero to 103

CFU/L). No cases of hospital-acquired legionellosis occurred during the study period. 

• Marchesi et al. (2011) compared the performance of treatment alternatives for controlling 

Legionella contamination in hospital hot water systems, including two hot water plants 

that installed chlorine dioxide treatment systems in 2005. Chlorine dioxide successfully 

maintained Legionella levels at <100 CFU/L. Electric boilers and POU filters had better 

performance than chlorine dioxide.4 The authors suggested implementing chlorine 

dioxide and electric boilers in parallel to control Legionella. 

• Zhang et al. (2009) evaluated using chlorine dioxide to treat for L. pneumophila in two 

hospitals reporting cases of hospital-acquired legionellosis. Water quality parameters 

were very similar between the two systems, except pH was 7.70 for Hospital A and 8.57 

for Hospital B. Hospital B had previously tried a superheat-and-flush of the hot water 

system and replacing a storage tank that was colonized with Legionella, but those 

 

4 The electric boilers were installed on cold water lines in high risk areas; each boiler served one to two patient 

rooms.
Draft – Technologies for Legionella Control: 

Scientific Literature Review 33 October 2015 

measures were unsuccessful. Chlorine dioxide was injected into the cold water main at a 

dosage rate of 0.5–0.7 mg/L to control Legionella and maintain chlorite levels below the 

MCL at both hot and cold water taps. The residual concentration for chlorine dioxide at 

the distal sites varied from zero to 0.11 mg/L depending on the building, date and type of 

tap (hot or cold). The occurrence of Legionella at hot water taps decreased from 60 

percent of sampling sites before chlorine dioxide addition to ≤10 percent of sampling 

sites after treatment; however, a significant decrease in the concentration of Legionella in 

positive samples was not observed. No cases of hospital-acquired Legionnaires’ disease 

were detected after installation of the chlorine dioxide system. 

• Sidari et al. (2004) reported on the first controlled field evaluation in the United States of 

a chlorine dioxide treatment system installed in June 2000, at a hospital linked to three 

cases of hospital-acquired Legionnaires’ disease. Legionella was eradicated (i.e., the 

authors had no positive results) from the hot water system, but only after 20 months of 

treatment. Rates of positive Legionella detections decreased significantly, from 23 

percent to 12 percent for hot water taps, and to almost zero percent for the cold water 

reservoir. Average chlorine dioxide residuals were 88 percent lower for the hot water tap 

than the cold, or 0.08 mg/L and 0.68 mg/L, respectively. No cases of Legionnaires’ 

disease occurred after the chlorine dioxide treatment system was installed. 

2.3.3.2 Potential Water Quality Issues 

Chlorine dioxide does not form the high levels of chlorinated DBPs that chlorination does (Gates 

et al., 2009). Chlorite and chlorate are the most prominent byproducts of chlorine dioxide (Gates 

et al., 2009). Chlorite could cause anemia in some people and affect the nervous systems of some 

infants, young children and fetuses of pregnant women. Ongoing exposure to chlorate ion can 

lead to an enlarged thyroid (USEPA, 2012). In an Italian hospital where chlorine dioxide was 

used to control Legionella in the hot water supply, chlorite levels higher than 0.7 mg/L were 

measured when the chlorine dioxide residual was >0.3 mg/L (Marchesi et al., 2013). In another 

study (Zhang et al., 2009), chlorine dioxide concentrations among different sampling locations 

over two years ranged from zero to 0.70 mg/L, whereas chlorite concentrations ranged from zero

to 0.82 mg/L. The average chlorate concentrations in hot and cold water were below the 

detection limit of 0.10 mg/L.

Water treatment utilities use chlorine dioxide for taste and odor control; however, various odors 

were reported when chloride dioxide residuals exceeded 0.05 mg/L in the winter or 0.15 mg/L in 

the summer (Gates et al., 2009). Kerosene-like and cat-urine-like odors were reported in some 

homes with new carpets when volatizing chlorine dioxide reacted with airborne volatiles 

(Dietrich and Hoehn, 1991). The taste and odor threshold for chlorine dioxide in water has been 

reported to be as low as 0.2 mg/L (Roche and Benanou, 2007). 

Chlorine dioxide is considered less corrosive than chlorine (Lin et al., 2011b). Some reports 

suggest that chlorine dioxide can cause damages to polyethylene pipes (Chord et al., 2011; Yu et 

al., 2011); however, information on other types of pipes is sparse (Gates et al., 2009). 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 34 October 2015 

2.3.3.3 Operational Conditions 

Parameter Conditions Indicating Operational Effectiveness 

Dosage rate is an important design criterion for chlorine dioxide disinfection systems. Chlorine 

dioxide dosage rates of 0.4 to 0.7 mg/L were reported by systems experiencing successful 

treatment performance (HSE, 2014; Casini et al., 2014; Marchesi et al., 2013; Zhang et al., 

2009). Zhang et al. (2009) reported that the dosage rate was between 0.5 and 0.7 mg/L depending 

on the flow rate of cold water entering the buildings. 

The required disinfectant dosage rate is dependent on system-specific conditions including pipe 

material and condition, the water’s disinfectant demand, the extent of biofilm on pipe surfaces, 

pipe diameter and length, complexity of the building water system, treatment goals (e.g., 

Legionella control), and the water turnover rate. For example, corrosion of galvanized piping can 

increase the water’s disinfectant demand and reduce the residual chlorine dioxide level (Lin et

al., 2011b). One study (Zhang et al., 2009) reported the chlorine dioxide demand of the building 

water was determined to be 0.20 mg/L after six hours of contact time at 23 degrees C (73.4 

degrees F) and pH 7.8. 

Maintaining a total chlorine dioxide residual of 0.1–0.5 mg/L at the tap is usually sufficient to 

control Legionella, although higher residuals may be necessary in a heavily colonized system 

(HSE, 2014). Some systems have established a treatment goal of maintaining a minimum 

chlorine dioxide residual of 0.3 mg/L at distal taps (Marchesi et al., 2013; Cristino et al., 2012; 

Sidari et al., 2004). If treatment with a residual higher than 0.8 mg/L is determined to be 

necessary, the facility may want to ensure that emergency disinfection procedures are developed 

and followed so that human consumption of a concentration of chlorine dioxide greater than the 

MRDL does not occur. 

Several studies identified factors that limited the effective performance of chlorine dioxide 

disinfection for Legionella control: 

• Casini et al. (2014) reported that performance of a hospital water system appeared to be 

affected by an accidental event in a water tank of the municipal water system that caused 

sediment buildup and increased water contamination in the hospital water system. After 

the event in December 2006, no further reduction in Legionella colonization was 

observed with only disinfection treatment. As a result, the hospital modified its WSP to 

include POU filtration with 0.2-μm sterile filters in critical areas of the system (e.g., 

intensive care units (ICUs), transplant wards). 

• Marchesi et al. (2013) reported that some samples associated with the chlorine dioxide 

treatment systems had chlorite levels higher than the Italian regulatory limit of 0.7 mg/L. 

Such exceedances would occur when the chlorine dioxide residual was >0.30 mg/L at 

distal taps. Because successful treatment performance (stated above) was based on 

maintaining a chlorine dioxide residual >0.30 mg/L at distal taps, this case highlights the 

importance of balancing disinfection needs with minimizing DBP formation.
Draft – Technologies for Legionella Control: 

Scientific Literature Review 35 October 2015 

• The lack of proper monitoring for a chlorine dioxide treatment system for drinking water 

was noted at a New York heath care facility after it experienced a Legionella outbreak in 

2010 (CDC, 2013b). Two hospitalizations for acute respiratory illness were reported and 

no deaths occurred. 

• Zhang et al. (2009) noted the importance of achieving an adequate disinfectant residual 

and its effect on the amount of time needed to control Legionella. Disinfection systems 

installed at Hospital A (January 2003) and Hospital B (April 2004) injected chlorine 

dioxide at the cold water service line to each building using a dosage rate of 0.5–0.7 

mg/L. Although both hospitals achieved significant reductions in Legionella occurrence

in the hot water system, Hospital B achieved control after six to 10 months of treatment, 

whereas Hospital A required 18 months. The longer treatment period for Hospital A was 

attributed to the longer time needed to achieve a chlorine dioxide residual >0.10 mg/L. 

• Sidari et al. (2004) reported differences in the time required to eradicate Legionella in a 

hospital’s hot and cold water systems after a chlorine dioxide treatment system was 

installed in June 2000. The water treatment goal was to achieve a minimum chlorine 

dioxide residual of 0.3 mg/L at distal sites. Chlorine dioxide residuals in the hot water 

loop averaged 0.08 mg/L (88 percent lower) compared to an average of 0.33 mg/L at cold 

water taps, which may explain why 20 months of treatment was required to eradicate 

(i.e., achieve zero occurrence) Legionella from the hot water system, whereas only 15 

months of treatment was needed for the cold water system.

Installation Considerations 

The location of disinfectant application point(s) is a critical design decision. The location may 

affect the required dosage rate and the time needed to inactivate Legionella. For example, if 

chlorine dioxide is added at the cold water service entry point to the building, the dosage rate 

should be sufficient to achieve an adequate disinfectant residual at hot water taps at distant points 

in the building. However, the need to comply with drinking water standards may drive a design 

decision to install multiple treatment units in the building system.

Monitoring Frequency and Location 

The SWTR (USEPA, 1989a) requires that all PWSs using chlorine dioxide monitor the level of 

residual disinfectant present in the water supply. The Stage 1 DBPR also requires that these 

PWSs monitor daily at each entry point to the distribution system to ensure it is not exceeding 

the MRDL (USEPA, 1998). Chlorine dioxide is a contaminant with acute health effects. Chlorine 

dioxide has a short sample hold time and should be measured immediately after sample 

collection; therefore, under the Stage 1 DBPR, on-site analysis at the water system is required.

If the daily chlorine dioxide measurement exceeds 0.8 mg/L, three follow-up distribution system 

chlorine dioxide samples must be measured the following day, as required by the Stage 1 DBPR. 

The Stage 1 DBPR and Stage 2 DBPR require that all PWSs using chlorine dioxide monitor 

chlorite for compliance with the MCL (USEPA, 2006c). Chlorite must be monitored daily at the 

entry point to the distribution system, in addition to being measured in a three-sample set each 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 36 October 2015 

month in the distribution system as detailed in the Code of Federal Regulations (CFR) at 40 CFR 

141.132(b)(2). Daily monitoring can be conducted on-site; monthly monitoring should be 

conducted at a certified laboratory (see Table Footnote 8 in 40 CFR 141.131(b)). 

Maintenance Needs 

Operating and maintenance practices for chlorine dioxide disinfection systems include 

maintenance of a disinfectant residual, regular system cleaning and flushing, inspections, and 

water quality monitoring. A newly constructed or rehabilitated piping system should be cleaned 

and flushed prior to initial disinfection (GLUMRBSPPHEM, 2012). Routine flushing and water 

quality monitoring are recommended to assure that adequate disinfectant levels are maintained 

throughout the building water system (HSE, 2014; Rosenblatt and McCoy, 2014). 

2.3.4 Copper-Silver Ionization 

2.3.4.1 Background 

Commercially available CSI systems typically consist of flow cells that contain metal bars or 

anodes (containing copper and silver metals) surrounding a central chamber, through which 

piped water flows. A direct electric current is passed between these anodes, releasing the copper 

and silver ions into the water stream. The amount of ions released depends on the composition of 

the anode and is controlled by the electrical current applied to the bars and the water flow rate. 

The earliest reports of CSI’s antibacterial properties were published in the mid-1970s (Spadaro et 

al., 1974; Berger et al., 1976). The earliest combined use of copper and silver ions as water 

treatment focused on the disinfection of swimming pools (Yahya et al., 1989) as an alternative to 

using high levels of chlorine. A 1994 report on the use of CSI treatment was the first to address

the efficacy of this treatment for controlling Legionella in hospital water systems (Liu et al., 

1994). CSI systems are currently used in buildings with complex water systems to control the 

growth and occurrence of Legionella bacteria. Lin et al. (2011b) documented CSI applications 

eradicating Legionella from hospitals worldwide. 

2.3.4.2 Characterization of Treatment Technology Effectiveness against Legionella 

Case studies constitute the majority of the published reports on the efficacy of CSI in controlling 

Legionella in building water systems (Chen, 2008; Mòdol et al., 2007; Blanc et al., 2005; Stout 

and Yu, 2003; Kusnetsov et al., 2001; Rohr et al., 1999; Liu et al., 1998; States et al., 1998; Liu 

et al., 1994). The studies generally describe situations where Legionella bacteria were found in a 

building water system and CSI was initiated in an attempt at Legionella control. Many of the 

reviewed laboratory studies indicate that copper and silver ions can reduce the cultivability of 

Legionella and the incidence of legionellosis. However, as with other technologies, other studies 

showed that Legionella can be protected from copper and silver ions when it is associated with 

biofilms or amoebae. The potential for Legionella to develop resistance to copper and silver ions 

has also been suggested by several studies.

• Lin et al. (1996) and Landeen et al. (1989) indicate that copper ions (at 0.4 mg/L) and 

silver ions (at 0.04 mg/L) can effectively reduce the cultivability of Legionella bacteria. 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 37 October 2015 

A 3- to 4-log (99.9 to 99.99 percent) reduction of culturable Legionella bacteria at these 

ion concentrations is reported to occur at pH 7.0–7.3, with exposure times reported to be 

<1 hour to 24 hours (Lin et al., 2002; Lin et al., 1996 and Landeen et al., 1989). 

• Hwang et al. (2007) showed that Legionella bacteria that are ingested by amoebae (in 

biofilms along piping walls) are protected from inactivation by copper and silver ions; a 

concentration of copper and silver that would normally result in a 7-log reduction of 

planktonic Legionella in 30 minutes would not similarly affect Legionella bacteria inside 

an amoeba, where they can survive for many days. 

• States et al. (1998) reported that CSI treatment was successful in reducing the percentage 

of samples testing positive for Legionella from 100 percent to less than 17 percent on 

average over a two-year period. 

• Kusnetsov et al. (2001) reported a 100-fold decrease in culturable Legionella from 

biofilm samples after CSI treatment was employed. 

• Rohr (1999) indicated an initial impact on Legionella occurrence, where 100 percent of 

sampling sites were positive for Legionella before treatment and 55 percent of sampling 

sites had positive results one year after treatment was initiated. Over the next three years, 

75–78 percent of samples were positive for Legionella. 

• Mòdol et al. (2007) described how a large hospital experienced success in decreasing the 

number of positive Legionella samples after initiating CSI, only to see the number of 

positive samples increase from 20 percent to 65 percent during two months when the 

treatment system was under repair. 

• Blanc et al. (2005) reported that the addition of copper and silver ions alone had no 

impact on the number of Legionella-positive water and biofilm samples in a large 

hospital. 

 

• Survey results by Stout and Yu (2003) showed that of 13 hospitals reporting at least 30

percent Legionella-positive samples before CSI treatment began, nine hospitals reported 

a sustainable (over a period of 6–9 years) decrease in the number of Legionella-positive 

samples; five hospitals reported no positive samples after treatment. This survey also 

showed that all of the hospitals reported cases of hospital-associated Legionnaires’ 

disease before CSI treatment, and all but one reported no cases after treatment. 

Other studies have reported the potential occurrence of Legionella strains that appear to be less 

sensitive to the toxic effects of certain chemicals such as copper and silver. Microorganisms are 

highly adaptive, and it is well documented that within the bacterial world there are cellular

mechanisms which allow bacteria to survive hostile environments. 

There is an understanding of how bacterial gene systems can confer resistance to copper and 

silver (Nies, 1999). Some of these gene systems are found in Legionella (Bondarczuk and 

Piotrowska-Seget, 2013). One common resistance mechanism in gram-negative bacteria (such as 

Legionella) requires an energy-dependent protein that protects the cell by acting as a pump to 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 38 October 2015 

export copper ions out of the cell (Bondarczuk and Piotrowska-Seget, 2013). The occurrence of 

Legionella strains tolerant of copper and silver at the levels employed in CSI treatment has been 

noted (Rohr et al., 1999). Hypochlorous acid, the active disinfecting chlorine species, is in part 

toxic to bacterial cells by virtue of interfering with the production of energy (in the form of 

adenosine triphosphate (ATP)) that is needed for many cellular processes including heavy metal 

resistance enzymes (Barrette et al., 1989). The synergy between free chlorine and heavy metal 

ions on Legionella copper resistance mechanisms and Legionella susceptibility is generally 

unstudied. However, Landeen et al. (1989) showed increased (although not statistically 

significant) inactivation rates of Legionella with copper and silver ions in the presence of 0.4 

mg/L free chlorine.

2.3.4.3 Potential Water Quality Issues 

Use of CSI may result in corrosion. Investigations have shown that test systems that exposed 

galvanized and mild steel (i.e., carbon steel) coupons to CSI resulted in corrosion (Loret et al., 

2005). The authors noted that copper deposition resulted in extensive pitting in ferrous materials 

via localized galvanic corrosion events. Copper coupons in the same system were covered with 

copper deposits at pH 7.6. Some evaluation of deposition, pitting and corrosion of copper piping 

in a system using CSI was presented by Boffardi and Hannigan (2013). Both the presence of 

additional copper ions and the pre-existing water conditions appeared to contribute to Type III 

pitting corrosion. This type of pitting usually occurs in soft water with alkaline pH >8.0 

(Edwards et al., 1994), at distal or stagnant locations, and at moderately warm temperatures 

(Boffardi and Hannigan, 2013; Edwards et al., 1994). Lytle and Schock (2008) found that waters 

with high pH (pH 9 and possibly as low as 8), low dissolved inorganic carbon (<10 mg/L and 

possibly as high as 25 mg/L) and chloride levels of 14–38 mg/L promoted pitting corrosion.

Materials compatibility and water quality will dictate the severity of corrosion, and awareness of 

the types of materials and water chemistry in a building water system is critical to maintaining 

system integrity.

High concentrations of both copper and silver have been reported in systems employing CSI, to 

levels approaching the maximum contaminant level goal and action level for copper (1.3 mg/L) 

and the secondary maximum contaminant level (SMCL) for silver (0.1 mg/L). (States at al., 

1998; Rohr et al., 1999). As copper levels in copper piping can rise during periods of stagnation, 

high levels of copper can occur in early morning first-draw water samples (Araya et al., 2004; 

Araya et al., 2003a; Araya et al., 2003b; Araya et al., 2003c; Araya et al., 2001; Knobeloch et al., 

1994). Copper, but not silver, was found to concentrate on biofilm material in building water 

systems employing CSI treatment (Liu et al., 1998; Zevenhuizen et al., 1979). 

Copper toxicity from ingestion of drinking water has been reported even without the contribution 

of copper from CSI systems (Araya et al., 2004; Araya et al., 2003a; Araya et al., 2003b; Araya 

et al., 2001; Knobeloch et al., 1998; Knobeloch et al., 1994). Symptoms of copper toxicity 

include nausea, abdominal cramps, vomiting and diarrhea. 

Both copper and silver can have negative aesthetic effects on water: color, taste and odor, and 

staining issues (Hong et al., 2010; Dietrich, 2009; Stout and Yu, 2003; Edwards et al., 2000; 

Knobeloch et al., 1998; Knobeloch et al., 1994). Edwards et al. (2000) attributed the rare 

occurrence of blue water to corrosion of copper plumbing; no other causative factors have been 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 39 October 2015 

identified. Ingesting high levels of silver can also lead to a skin discoloration condition called 

“argyria” (Drake and Hazelwood, 2005; WHO, 1996; USEPA, 1989b). According to WHO 

(2003), the lowest dose of silver that may lead to occurrence of argyria has not been determined, 

but, in general, silver levels up to 0.1 mg/L can be tolerated without risk to health. Silver levels 

approaching the SMCL of 0.1 mg/L have been reported in building water systems using CSI 

treatment (Rohr et al., 1999; States et al., 1998). 

Laboratory studies have been conducted on the effectiveness of CSI in reducing levels of other 

bacterial species commonly found in built environments, including Pseudomonas, 

Stenotrophomonas, Acinetobacter (all gram-negative bacteria like Legionella) and 

Mycobacterium. These studies showed that Legionella are as much as 10-fold more sensitive to 

copper than Pseudomonas, Stenotrophomonas and Acinetobacter, but that Legionella are less 

sensitive to silver than Pseudomonas and Stenotrophomonas (Huang et al., 2008; Hwang et al., 

2007). Copper and silver ions appear to act synergistically (the total effect is greater than the sum 

of the individual effects) toward Legionella (Lin et al., 1996), Pseudomonas and Acinetobacter

(Huang et al., 2008), while the ions act antagonistically (the interaction of the two metals lessens 

the effect of each metal acting individually) toward Stenotrophomonas (Huang et al., 2008). 

Mycobacterium was shown to be 100-fold less sensitive to copper and silver ions than Legionella

(Lin et al., 1998b), and copper and silver levels that controlled Legionella were unable to control 

the occurrence of Mycobacterium in a hospital building water system (Kusnetsov et al., 2001). 

Field studies of CSI have reported some effectiveness in reducing fungi in hospital water 

systems, especially Fusarium spp. (Chen et al., 2013). A report on healthcare facilities in Spain 

with (n=9) and without (n=7) ionization treatment systems cited a fungal isolation rate of 28 

percent versus 77 percent, respectively (Pedro-Botet et al., 2007). CSI has not been reported to 

reduce levels of heterotrophic bacteria or amoebae in either a controlled laboratory study (Rohr 

et al., 2000) or a case study (States et al., 1998). 

2.3.4.4 Operational Conditions

Parameter Conditions Indicating Operational Effectiveness

Several physicochemical parameters that could impact treatment effectiveness are discussed in 

more detail below. 

Maintaining copper and silver at the levels recommended by the manufacturer is a best practice 

in achieving operation effectiveness. Note that monitoring typically includes measurement of the

total metal concentration, which includes copper and silver that are bound up as complexes, as 

well as copper and silver ions. The presence of copper and silver ions is thought to be critical for 

treatment effectiveness, so maintaining proper pH and avoiding interfering materials (e.g.,

phosphates, chlorides) is also important (Zevenhuizen et al., 1979). Phosphates, such as those 

added for corrosion control, can bind to copper ions as well as silver ions, reducing their 

treatment effectiveness (Zevenhuizen et al., 1979). It has also been reported that in the presence 

of 20–40 mg/L of chloride ions, silver ion levels are significantly (60 percent) decreased by 

complexing with chloride (and are presumably less microbiocidal) (Lin et al., 2002). 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 40 October 2015 

The presence of dissolved organic carbon at 2 mg/L, calcium at 100 mg/L, magnesium at 80

mg/L and bicarbonate at 150 mg/L did not appear to decrease the treatment efficacy of copper 

and silver ions against Legionella in a laboratory study (Lin et al., 2002). 

The impact of pH on the ionic nature (and thus the microbiocidal action) of copper in solution is 

also important. At a pH of 7, exposure to 0.4 mg/L of copper resulted in a 4-log (99.99 percent) 

reduction of culturable Legionella in one hour in a controlled laboratory study (Lin et al., 2002); 

however, at a pH of 9, there was no appreciable decrease in culturable Legionella over the same 

period of time with the same copper exposure. At pH levels >6.0, copper forms insoluble 

complexes with a number of compounds. While in the pH range typical of potable waters (pH 6 

– 9), silver ions are not diminished. 

With regard to the effects of temperature, one study (Landeen et al., 1989) found no significant 

difference in L. pneumophila inactivation rates in experiments conducted at room temperature 

(21–23 degrees C, or 69.8–73.4 degrees F) and elevated temperature (39–40 degrees C, or 

102.2–104 degrees F) using water with 0.2 mg/L free chlorine, with or without 400 μg/L of 

copper and 40 μg/L of silver. 

Installation Considerations 

CSI systems can be plumbed into either the cold water entry pipe or plumbed into the hot water 

line. Care should be taken to install devices downstream of any process that will remove or 

exchange copper and silver ions. Note that construction that includes new copper pipe can add 

copper to water for a time via leaching. 

Newly installed CSI systems generally require a period of time to adjust system output in order 

to achieve the desired level of metal ions. Representatives from the manufacturer are typically 

involved in on-site start-up and balancing of the system. 

Monitoring Frequency and Location 

Initial monitoring during start-up is critical to ensure the copper action level in the Lead and 

Copper Rule is not exceeded. A facility that is considering installation of CSI should consult 

with their primacy agency to determine a protocol for initial monitoring. During the initiation of 

CSI, weekly monitoring with inductively coupled plasma/mass spectrometry (ICP/MS) (e.g., 

EPA Method 200.8) or atomic absorption spectroscopy (e.g., Standard Methods 3111B) can be 

conducted to determine accurate levels of copper and silver.

5 As treatment proceeds, the 

frequency of analysis may be reduced, but these methods remain the only reliable and accurate 

means to determine copper and silver concentrations. 

Operational monitoring of copper is generally conducted weekly at a variety of locations 

throughout the building water system to monitor for process changes in copper concentration, 

high copper concentrations that may be indicative of improper application, and no detectable 

copper. Handheld colorimeters and reagents are available for monitoring copper in the field but 

 

5 The National Environmental Methods Index (https://www.nemi.gov/home/) “is a searchable database that allows 

scientists and managers to find and compare analytical and field methods for all phases of environmental 

monitoring.”
Draft – Technologies for Legionella Control: 

Scientific Literature Review 41 October 2015 

laboratory analysis is needed to confirm field measurements (Sidari et al., 2014). These wet 

chemical tests have practical limits on detection when near the lower limit of detection (0.04 

mg/L). These field methods are not approved for compliance monitoring. 

According to the United Kingdom Health and Safety Executive (2014), both copper and silver

levels should be monitored monthly, or no less than quarterly, at the same locations within the 

building, using appropriate sampling procedures and submitted for analysis by ICP/MS or atomic 

absorption (HSE, 2014). Sampling locations will vary in specific buildings and should include 

both taps that are frequently and infrequently used. When appropriate, the facility operator 

should work with the primacy agency to determine a site sampling plan for the water system.

First-draw and flushed samples will often yield different results (Liu et al., 1994). First-draw 

sample testing can indicate how periods of low water flow may affect metal levels given the 

water quality conditions found in a specific building, while flush samples will measure the metal 

levels in the main cold or hot water lines feeding individual taps. Knowledge of how water flows 

in any particular building is essential in determining the best monitoring frequency and locations. 

Maintenance Needs

The copper- and silver-containing anodes are sacrificial and should be rehabilitated periodically 

as they become smaller, according to the recommendations of the manufacturer. Anodes can also 

wear down due to high shear velocities (Chen et al., 2008). The anodes typically will develop 

scale from calcium in all but the softest waters and should be cleaned by scraping/acid treatment

on a regular basis. Scale build-up reduces the surface area from which ions can be released, 

lowering the ion output. Any time a component of a water system is opened to the environment 

for maintenance, such as scraping, procedures should ensure that the system components are reinstalled in a sanitary condition (i.e., disinfected). 

Regular flushing of water lines (either through the frequent use of taps or routine weekly 

flushing) was cited as a critical factor in maintaining the effectiveness of CSI systems 

(Kusnetsov et al., 2001; Liu et al., 1994). 

2.3.5 Ultraviolet Light Disinfection

2.3.5.1 Background 

UV disinfection is a well-established treatment technology for inactivating pathogens present in 

the environment. 

In the drinking water context, UV disinfection was initially most widely used in Europe, with 

hundreds of installations in place by 1985 (USEPA, 2006e). In North America, UV disinfection 

has been more widely employed in drinking water applications since 2000 to address health 

concerns associated with Cryptosporidium. As of the spring of 2008, there were at least 300 

water systems in the United States and Canada with UV installations treating flows >350 gallons 

per minute (Wright et al., 2012). 

UV reactor validation helps to define the operational conditions under which the pathogens of 

concern are inactivated. Validation is a method of determining the operating conditions under 

which a UV reactor delivers a specified dose. This generally involves initial tests using a 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 42 October 2015 

surrogate organism (e.g., bacteriophage MS2) rather than the target pathogen (e.g., 

Cryptosporidium) to establish the dose relationship between the two organisms. This bioassay 

helps determine the dose required for full-scale testing using the surrogate. The conditions that 

are examined for full-scale testing to establish dose are flow rate, UV transmittance (UVT) (a 

measure of the fraction of incident light transmitted through a material) and lamp output. The 

EPA has developed guidance for validation of UV reactors (USEPA, 2006e). Independent 

organizations have used this EPA guidance to develop their own validation approaches. There 

are also several validation standards for UV reactors from organizations based in Austria 

(Österreichisches Normungsinstitut – ÖNORM) and Germany (Deutsche Vereinigung des Gasund Wasserfaches – DVGW) that are widely accepted and use a benchmark UV dose of 40 

millijoules per square centimeter (mJ/cm2) (GLUMRBSPPHEM, 2012). 

There are two methods for validating UV units. In short, the setpoint approach establishes a 

measured UV intensity that corresponds to a specific dose and flow rate. The dose control 

method (also referred to as the calculated dose approach) provides a means of determining the 

required intensity that corresponds to a specific flow rate, UVT and dose. For applications 

related to Legionella control in buildings and other moderately sized facilities, reactors using the 

setpoint approach will likely be installed due to the ease of operations and control. 

2.3.5.2 Characterization of Effectiveness against Legionella

There are several important lessons from installations of UV disinfection in hospital settings and 

UV installations in general:

• UV disinfection has been shown to be effective at decreasing and, in some cases, 

eliminating Legionella from facility piping.

• UV is only effective at inactivating Legionella in the water that flows through the UV 

reactor. For existing facilities with Legionella that is present in the piping systems

downstream of a UV reactor, supplemental controls such as thermal treatment or 

chemical disinfection will be necessary. 

• UV reactors need to be maintained to remain effective. The quartz sleeves that house the 

reactors can be fouled by iron, manganese, calcium carbonate or other deposits that 

decrease UV output. Lamps and other reactor components also need to be replaced 

periodically in order to maintain treatment effectiveness. 

Relatively low UV doses appear to inactivate L. pneumophila (Exhibit 2-3). A dose of 1 mJ/cm2

was found adequate to achieve 99 percent (2-log) reduction in six different Legionella spp. using 

irradiation times from 33 to 63 minutes depending on the species (Gilpin et al., 1985). A dose of 

30 mJ/cm2

 achieved 99.999 percent (5-log) reduction in 20 minutes in a model building water 

system (Muraca et al., 1987). 

Usually, there are limited opportunities for exposure to light for water treated and held in 

building water systems. However, if there is a significant opportunity for light repair (repair of 

UV-induced DNA damage using photoreactivating light), such as in water used in tubs, pools 

and baths, a higher UV dose should be considered. At a UV dose adequate to achieve 99.9 

percent (3-log) reduction of Legionella, subsequent exposure to fluorescent light for one hour 

resulted in only a 68 percent (0.5-log) reduction following initial inactivation by low pressure

UV lamps and only 60 percent (0.4-log) reduction following inactivation by medium pressure
Draft – Technologies for Legionella Control: 

Scientific Literature Review 43 October 2015 

UV lamps (Oguma et al., 2004). Similar significant light-repair of Legionella has been observed 

by others (Knudson, 1985). 

Exhibit 2-3: UV doses (mJ/cm2) for inactivation of L. pneumophila

L. pneumophila

strain

Lamp 

Type 1-log 2-log 3-log 4-log Reference

Philadelphia Type 2 LP 0.92 1.84 2.76 No data Antopol and Ellner, 

1979

Philadelphia 1 

(no light repair) LP 0.5 1.0 1.6 No data Knudson, 1985

Philadelphia 1 

(with light repair) LP 2.3 3.5 4.6 No data Knudson, 1985

Philadelphia 1

ATCC33152 LP 1.6 3.2 4.8 6.5 Oguma et al., 2004

Philadelphia 1

ATCC33152 MP 1.9 3.8 5.8 7.7 Oguma et al., 2004

ATCC43660 LP 3.1 5.0 6.9 9.4 Wilson et al., 19921

Notes:

LP = Low pressure lamps, which have a single output of UV peaking around a wavelength of 254 nanometers. 

MP = Medium pressure lamps, which have polychromatic (or broad spectrum) output of UV at multiple wavelengths. 1 As reported by Wright et al. 2012.

Given the sensitivity of Legionella to UV disinfection, a well-maintained UV disinfection system 

can be effective at significantly decreasing the presence of Legionella in building water systems 

to less than 10 CFU/mL (Franzin et al., 2002; Liu et al., 1995). In the case of one new facility, a 

UV disinfection unit was installed on the incoming water supply, and none of the 930 cultures of 

hospital water were positive. In addition, there were no confirmed hospital-acquired Legionella

infections over a 13-year study period (Hall et al., 2003). UV disinfection may not be effective in 

pipe systems that have been colonized by bacteria. One study found no statistical difference in 

showers treated with UV and those not treated. However, Liu et al. (1995) showed that when the 

lines were disinfected, the UV treated showers remained Legionella-free for a month, while the 

untreated showers were recolonized by Legionella within a week. 

Fouling of the UV lamps was found to decrease effectiveness of the UV treatment. Legionella

recolonized showers treated with UV after one month of operation, but when filters were added 

to remove particles that foul the UV lamps, the showers remained Legionella-free for a period of 

three months (Liu et al., 1995). 

2.3.5.3 Potential Water Quality Issues

Water quality data is needed to adequately characterize the water to be treated by the UV reactor

and identify any pre-treatment that may be required. Manufacturers may have their own data 

requests, though the following list will cover most water quality information needed (Alaska 

DEC, 2014; AWWA, 2012; GLUMRBSPPHEM, 2012; WSDOH, 2009; USEPA, 2006e): 

• Temperature - Some reactor components may not be tolerant of water >35 degrees C (95 

degrees F). For this reason, UV should be installed on the cold water supply upstream of 

water heaters and continuous hot water recirculation loops. 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 44 October 2015 

• Disinfectant type and residual - Some reactor components may not be tolerant of certain 

disinfectants or high doses, so UV equipment manufacturers should be consulted about 

exposure of UV reactors to chemical disinfectants. 

• UVT - Components in the water can absorb UV light and reduce the dose delivered to the 

microorganisms from the UV reactor. UVT (also measured as UV absorbance) is a key 

parameter in making sure that the UV reactor is properly sized for the facility. 

• Iron and manganese - These constituents can foul quartz sleeves, leading to decreased 

UV output. Iron concentrations >0.1 mg/L may cause operational issues. 

• Hardness - Calcium and magnesium salts may precipitate on quartz sleeves leading to 

decreased UV output. A hardness of >120 mg/L is a threshold of concern 

(GLUMRBSPPHEM, 2012). 

2.3.5.4 Operational Conditions

Parameter Conditions Indicating Operational Effectiveness

The operation of a small UV reactor is typically governed by two key parameters: the flow 

through the reactor and UV sensor reading(s). Over time, UV sensors will drift out of calibration. 

For this reason, the readings from a UV duty sensor installed in the reactor should be compared 

against a reference sensor temporarily inserted in the reactor. PWSs typically make these sensor 

checks on a monthly basis. If the calibration ratio between the duty and reference sensor readings 

is >1.2, then follow-up actions such as recalibration or replacement of the UV sensor should be 

taken (USEPA 2006e). 

Installation Considerations 

There are several sources of design guidance for the application of UV disinfection on potable 

water supplies (Alaska DEC, 2014; AWWA, 2012; GLUMRBSPPHEM, 2012; WSDOH, 2009; 

USEPA, 2006e). These references cover a range of applications from those producing only a few 

gallons per day to millions of gallons per day. The following checklist is tailored to institutional 

settings for Legionella control: 

• Hydraulics should allow for even flow through the reactor. Control valves and reducers 

should be avoided within five pipe diameters upstream of the UV reactor to avoid jetting 

and swirling flow through the UV reactor. 

• Redundancy includes providing more than one UV reactor to allow for chemical cleaning 

and equipment maintenance. 

• Valves to isolate UV reactors are necessary. In some cases, such as when UV reactors are 

flooded with cleaning chemicals, special valve arrangements, such as double-block-andbleed valves, may be required on the outlet and inlet piping. 

• Power quality analysis includes review of sub-second power interruptions and voltage 

sags at the location of a proposed UV installation. An uninterruptible power supply or 

power conditioning equipment may need to be considered.

• Alarm and reactor shutdown conditions should be clearly identified. 

• A lamp breakage response plan should be developed that defines emergency response 

actions that will be taken if a lamp breaks. Low velocity traps or other piping 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 45 October 2015 

configurations to collect broken lamp components should be considered. The potential for 

hydraulic transients should be evaluated because they may cause the quartz sleeves that 

house UV lamps to fail. 

Maintenance Needs

While UV reactors are relatively simple to maintain, compared to more complex treatment 

equipment, they do require routine maintenance to ensure that the UV dose remains adequate for 

inactivation of pathogens. Some of the basic maintenance items include cleaning the quartz 

sleeves housing the lamps and periodically replacing the lamps, as their output decreases with 

time. In addition, some reactor components can be affected by disinfectants, including chlorine, 

added prior to the reactor, and additional maintenance may be required. Most UV lamps installed 

in smaller reactors will typically be rated for 10,000–12,000 hours of operation (one year of 

continuous operation equals 8,736 hours). For a detailed list of recommended maintenance 

activities for a UV reactor, please see EPA’s Ultraviolet Disinfection Guidance Manual for the 

Final Long Term 2 Enhanced Surface Water Treatment Rule (USEPA, 2006e). 

2.3.6 Ozone

2.3.6.1 Background 

Ozone is used in drinking water treatment for disinfection and oxidation (USEPA, 1999d, 2007). 

It is generated on-site as a gas using either air or liquid oxygen and is then transferred (dissolved) 

into the water phase. When dissolved in water, molecular ozone (O3) is unstable and decomposes 

to hydroxyl radical, which is a stronger and typically more reactive oxidizing agent than 

molecular ozone. Ozone decomposes quickly during water treatment (USEPA, 1999d, 2007). 

Therefore, during a typical ozonation process, both molecular ozone and the hydroxyl radical 

may contribute to the oxidation of contaminants of concern. The relative importance of these two 

oxidants depends on the concentrations of the oxidants and the reactivity of the contaminant with 

each oxidant.

The use of ozone in U.S. water treatment facilities has been increasing over the last four decades 

(Thompson et al., 2013). As an oxidant, ozone can be used to oxidize iron, manganese, taste and 

odor compounds, and DBP precursors. It can oxidize organic matter into smaller molecules that 

are more easily biodegradable. As a primary disinfectant, ozone is more effective than chlorine, 

chloramines and chlorine dioxide for inactivation of Cryptosporidium, Giardia and viruses 

(USEPA, 1999d, 2007). However, ozone cannot be used as a secondary disinfectant because it 

decays very rapidly and cannot maintain a residual in the distribution system (USEPA, 1999d, 

2007). 

2.3.6.2 Characterization of Effectiveness against Legionella 

Several researchers have reported rapid and effective inactivation of Legionella, mostly in 

laboratory studies (Edelstein et al., 1982; Muraca et al., 1987; Domingue et al., 1988; Jacangelo 

et al., 2002). They found little to no effect of pH (from 7.2–8.9), turbidity and temperature (from 

25–43 degrees C, or 77–109.4 degrees F) on ozone inactivation of L. pneumophila. However, 

information on ozone systems installed in hospitals and other types of buildings for L. 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 46 October 2015 

pneumophila control is lacking. Only one paper, by Edelstein et al. (1982), evaluated the efficacy 

of ozone for eradicating L. pneumophila in hospital plumbing fixtures, but the result of the study 

was inconclusive. 

• Edelstein et al (1982) applied continuous ozonation to the water supply in an unoccupied 

hospital building to evaluate whether it would eradicate L. pneumophila from the 

plumbing fixtures with positive cultures. The water supply was split into two wings: one 

treated with ozone, while the other was untreated. In their laboratory study using distilled 

water, more than 3-log reduction in L. pneumophila was achieved by exposure to 0.32 

mg/L of ozone for 20 minutes. However, results from ozonation of the water supply 

system (average ozone levels of 0.79 and 0.58 mg/L in two study phases, respectively) 

were difficult to interpret because the non-ozonated water in the control wing also 

showed inactivation of L. pneumophila due to a higher water usage rate and an 

unexpected rise in the chlorine residual in the control wing (average chlorine residual 

levels of 0.24 and 0.12 mg/L in two study phases, respectively). Although the treatment 

wing had a smaller number of positive cultures (3 of 12) than the control wing (8 of 12), 

the researchers could not reach a conclusion on the role of ozone in the inactivation of L. 

pneumophila. The study indicated that when ozonation was stopped, L. pneumophila

regrew and reached levels close to the pre-test conditions at the end of the stagnation 

phase. Moreover, the authors pointed out one important factor for continual dosing of 

ozone, namely that residual ozone at the faucet or shower head led to the release of 

gaseous ozone into the air (an issue discussed in Section 2.3.6.4). 

• Muraca et al. (1987) compared the efficacy of chlorine, heat, ozone and UV light for 

inactivating L. pneumophila in a bench-scale model plumbing system. Legionella was 

added to the system and allowed to circulate. Continuous ozonation for five hours at a 

concentration of 1 to 2 mg/L achieved a 5-log inactivation of L. pneumophila at 25 and 

43 degrees C (77 and 109.4 degree F, respectively). Neither turbidity nor the higher 

temperature (43 degrees C, or 109.4 degrees F) was reported to affect the efficacy of 

ozone. However, the conclusion regarding no effect of turbidity was drawn from a 

comparison between non-turbid water (tap water) and turbid water (containing 4 to 5 

mg/L of suspended solids, prepared by making 1:10 dilution of a concentrated hot-water 

tank effluent sample). The turbidity of neither water was measured or reported in the 

paper. The report of the insignificant effect of temperature on inactivation in this study 

may have more to do with the experimental design (in which log-inactivation was not 

actually measured as a function of CT) than the inherent temperature dependence of the 

ozone- L. pneumophila reaction.

• Domingue et al. (1988) conducted laboratory experiments to compare the bactericidal 

effects of ozone, hydrogen peroxide and free chlorine on “free” L. pneumophila cells. 

Ozone was the most potent of the three disinfectants, with a greater than 2-log kill of L. 

pneumophila occurring during a 5-minute exposure to 0.10–0.3 mg/L ozone. They also 

reported little to no effect of pH on ozone inactivation of L. pneumophila, with pH 

ranging from 7.2 to 8.9. Experiments were conducted at 25, 35 and 45 degree C, and 

slightly lower ozone doses were required at 35 and 45 degree C than at 25 degree C. At a 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 47 October 2015 

higher temperature, an enhanced rate of disinfection could have been offset by a higher 

rate of ozone decomposition. Overall, the effect of temperature in this work is not clear. 

• Jacangelo et al. (2002) conducted laboratory studies to evaluate multiple disinfectants, 

including ozone, for inactivation of waterborne emerging pathogens including 

Legionella. The ozone dose rate was 1.0 mg/L. The model-predicted CT values for a 2-

log inactivation of Legionella at pH 7 were 2.5, 0.16 and 1.1 min-mg/L at 5, 15 and 25 

degrees C (41, 59 and 77 degrees F), respectively. 

• Ruiz et al. (2007) designed and constructed a pilot plant to simulate the growth of 

Legionella in biofilms and to evaluate the use of ozone to reduce both Legionella and

biofilms. They discussed technical issues with the application of ozone for control of 

Legionella in water systems, including injection methods, automation systems, liquid and 

gas phase online measurements, and interaction of ozone with the structure of the facility. 

However, no test results were reported in this paper. 

2.3.6.3 Potential Water Quality Issues 

Ozone itself does not form halogenated DBPs such as THMs and HAAs. However, ozonation of 

water containing inorganic bromide can produce bromate, a regulated DBP with an MCL of 10 

μg/L. The disinfection process of a PWS will likely have transformed any bromide in water to 

organically bound bromine or inorganic bromamines. In either case, these forms of bromine are

less likely to contribute to bromate formation via an ozonation process in a building water 

system. As such, bromate formation may not be as relevant as in the water treatment plant. Other 

ozonation byproducts include aldehydes and organic acids that are more readily biodegradable

and that may contribute to assimilable organic carbon (AOC) and hence biological growth in the 

distribution system. In addition, these ozonation byproducts are more likely to form some types 

of DBPs upon chlorination or chloramination (Carlson and Amy, 2001; Shah and Mitch, 2012).

However, these general concepts regarding ozonation pertain to treatment of water at the plant. 

Ozonation of water that has already undergone treatment, including exposure to a chlorine or 

chloramine residual in the distribution system en route to the building (e.g., hospital) has not 

been studied to a great extent. Therefore, impacts of ozonation on AOC or DBP formation in a 

building water system are still unclear.

2.3.6.4 Operational Conditions 

Ozone disinfection is not typically impacted by pH in the range of 6 to 9. As water temperature 

increases, ozone disinfection efficiency increases (USEPA, 1999d). However, because ozone 

decomposes quickly in hot water, it is difficult to maintain an effective concentration throughout 

the system to control Legionella. Therefore, there is a need to balance the tradeoffs between 

potentially higher inactivation rates and lower CT with increased water temperature. Due to the 

faster decomposition of ozone in warm water, water leaving the ozone contactor with a 

concentration of 1 to 2 mg/L may not have a concentration high enough to inactivate Legionella

when it reaches distal parts of the system. 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 48 October 2015 

One important aspect of ozone-based treatment in a building is the potential for ozone residual 

that reaches the tap to degas from the water and expose building occupants to ozone gas. Ozone 

is a toxic gas (e.g., being a principal component of smog). Ozone is corrosive and can corrode 

steel pipes and fittings, concrete, rubber gaskets and other material it comes into contact with 

(USEPA, 2007). Due to safety concerns and the corrosiveness of ozone, on-site generation of 

ozone gas requires containment or a separate structure. Ambient air monitoring may also be 

required for compliance with local regulations. 

Ozone disinfection is a relatively complex process. Operational and maintenance demands are 

significantly greater than those for chlorine and chloramines (USEPA, 2007). 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 49 October 2015 

3 Other Strategies Used to Control for Legionella

3.1 Emergency Remediation

Emergency remediation of a building water system is triggered by an outbreak of legionellosis 

associated with a potable water system, identification of suspected cases of the disease associated 

with a potable water system, or identification of Legionella-positive water results during routine 

environmental testing (ASHRAE, 2015; Department of Veterans Affairs, 2014). Several

agencies and organizations have published standards or guidance documents on when and how to 

conduct emergency remediation (HSE, 2014; Department of Veterans Affairs, 2014; ASHRAE, 

2015; HSE, 2009; CDC, 2003; ASHRAE, 2000). Some of these documents apply to not only 

building water systems but also cooling towers and evaporative condensers; whirlpool spas; 

decorative fountains; and other aerosol-generating air coolers, humidifiers, and air washers. This 

chapter provides an overview of commonly used emergency remediation methods, including 

superheat-and-flush disinfection, shock hyperchlorination, POU filtration, and any combination 

of these methods. 

3.1.1 Superheat-and-Flush Disinfection 

3.1.1.1 Background 

The superheat-and-flush disinfection method involves raising the water temperature in the hot 

water heater sufficiently high to ensure hot water is delivered to outlets; circulating the hot water 

through all water outlets, faucets and showerheads; and then flushing with the hot water for a 

suitable period. Because Legionella can easily be killed at temperatures >60 degrees C (140 

degrees F), raising the temperature of hot water tanks to 71–77 degrees C (160–170 degrees F) 

and keeping the water temperature at outlets >65 degrees C (149 degrees F) during flushing are 

recommended (Department of Veterans Affairs, 2014; Sehulster and Chinn, 2003; ASHRAE, 

2000). The optimal flush time reported varies from 10 to 30 minutes depending on the 

characteristics of the building water system. A 30-minute flush, first adopted by Best et al. 

(1983), is recommended as a good practice (Department of Veterans Affairs, 2014). 

3.1.1.2 Characterization of Effectiveness against Legionella

The superheat-and-flush method can be effective as an emergency disinfection procedure for 

building hot water systems, particularly in hospital outbreak scenarios. 

• Best et al. (1983) first reported the use of superheat-and-flush to control Legionella from 

a hospital water supply by raising the temperature of hot water tanks as high as 77 

degrees C (170.6 degrees F) for 72 hours and flushing the water outlets for 30 minutes 

with hot water. After flushing, the number of samples testing positive for Legionella was

reduced, followed by a decline in the incidence of legionellosis. The temperature of the 

hot water storage tanks was intermittently increased on eight occasions to 60–77 degrees 

C (140–170.6 degrees F), resulting in a decrease in the number of months in which cases 

of Legionnaires’ disease occurred and the proportion of nosocomial pneumonias caused 

by L. pneumophila and Pittsburgh pneumonia agent. 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 50 October 2015 

• Darelid et al. (2002) reported the successful application of thermal shock disinfection 

after a 1991 nosocomial outbreak of Legionnaires’ disease in a Swedish hospital. The hot 

water temperature was raised from 45 degrees C to 65 degrees C (113 degrees F to 149 

degrees F) to maintain the circulating hot water temperature above 55 degrees C (131 

degrees F) to control the bacteria. Environmental monitoring was conducted over a 10-

year period to confirm whether this thermal shock treatment was sufficient or if chemical 

disinfection was required. The monitoring results showed that complete eradication of 

Legionella was not possible, but the occurrence of nosocomial Legionnaires’ disease was 

controlled by maintaining the circulating hot water temperature above 55 degrees C (131 

degrees F). 

However, an inadequate temperature for the superheat (below 65 degrees C, or 149 degrees F) or 

a short flush time (such as five minutes) is ineffective for the control of Legionella, as 

experienced at some hospitals (Chen et al., 2005). The shock treatment may not provide longterm control of Legionella if the building water system does not maintain a proper temperature or 

a residual chlorine level.

• Chen et al. (2005) conducted superheat-and-flush treatment on the water supply for a 

1,070-bed medical center in southern Taiwan. The treatment procedure involved 

removing faucet aerators and showerheads at distal sites; flushing distal sites with cold 

water for two minutes; and flushing distal sites with hot water at 60 degrees C for five 

minutes. The procedure was conducted once a day for five consecutive days on each 

portion of the water system. Water samples were collected before treatment and 10 days 

after treatment. The first heat and flush treatment, performed over an eight-week period, 

eliminated Legionella from patient wards and reduced the colonization rate in ICUs from 

80 percent to 25 percent. But two months later, the colonization rate had increased from 

zero to 15 percent in patient wards, and from 25 percent to 93 percent in the ICUs. The 

second superheat-and-flush treatment, performed over a 2-day period, resulted in much 

smaller reductions in the colonization rate. 

• Mietzner et al. (1997) conducted thermal treatment of a hot water circuit in a hospital by 

flushing hot water (>60 degrees C, or >140 degrees F) through distal fixtures for 10 

minutes. Sampling of the faucets showed that positive samples decreased from 

approximately 80 percent to 1 or 2 percent of samples immediately following the initial 

treatment, then increased to 36 percent within 61 days of the treatment. Three additional 

heat-flush treatments resulted in zero detection of Legionella. But recolonization 

occurred within 29 days of the last treatment. The heat-flush treatment failed to provide 

long-term control of Legionella.

Combining the superheat-and-flush method with supplemental continuous chlorination (Cristino 

et al., 2012; Heimberger et al., 1991; Snyder et al., 1990) or UV light irradiation (Liu et al., 

1995) has achieved some success in decontaminating hospital water systems. 

• Snyder et al. (1990) reported a successful application of heat flushing followed by 

continuous supplemental chlorination to reduce L. pneumophila in a hospital hot water 

system. Twelve of 74 sampling sites in the hot water system were culture-positive for L. 

pneumophila. Heat flushing (>60 degrees C, or >140 degrees F) at hot water system 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 51 October 2015 

outlets for 30 minutes alone reduced the number of Legionella positive samples by 66 

percent, but within four months, the number of positive samples had increased. 

Continuous supplemental chlorination was added to the hot water system at a dosage rate 

of 2 mg/L. After six weeks, the number of Legionella-positive samples decreased from 

37 percent (43 of 115 samples) to 7 percent (8 of 115 samples). After 17 months of 

continuous supplemental chlorination, no new cases of legionellosis had occurred. 

• Heimberger et al. (1991) reported the successful application of hot water flushing and 

supplemental chlorination to control Legionella at a tertiary care hospital in Syracuse, 

New York. L. pneumophila was found in 6 of 32 water samples including samples from 

one of two hot water tanks. Initial treatment of the hot water system included tank 

cleaning, hot water flushing and shock chlorination but did not include continuous 

supplemental chlorination. One month after initial treatment, L. pneumophila was again 

detected from a hot water tank and several taps, and another case of legionellosis 

occurred. In response, hot water flushing, shock chlorination and continuous 

supplemental chlorination were conducted. On a monthly basis, each hot water tank is 

taken offline, cleaned and treated with hot water. In the 7.5 months after these practices 

were employed, all samples were negative for Legionella and no new cases of 

legionellosis had occurred. 

• Cristino et al. (2012) reported the successful application of various shock disinfection 

methods (e.g., heat shock, chemical shock with peracetic acid and chlorine dioxide) 

followed by continuous chlorination for long-term care facilities, including three hot 

water systems that were colonized by L. pneumophila and one hot water system 

colonized by L. londiniensis. No cases of hospital-acquired legionellosis occurred during 

the study period. Although three of four systems reported that 100 percent of samples 

were positive for Legionella before and after shock treatment, the mean Legionella count 

was reduced by up to 69 percent as a result of shock disinfection. Two years of 

environmental monitoring after shock disinfection showed that Legionella counts either 

continued to decrease or remained at post-treatment levels. 

• Liu et al. (1995) conducted superheat-and-flush and shock chlorination treatment prior to 

UV treatment of a hospital’s hot and cold water systems. Five years of surveillance data 

at untreated control sites (three showers and 20 other water outlets) showed that 30–80 

percent of sites were persistently colonized with L. pneumophila (i.e., 1–300 CFU per 

swab). The UV treatment units were located near points of use such as showers. Filters 

were added to prevent scale accumulation on the UV lamps. The study showed that UV 

plus pre-filtration could prevent Legionella recolonization for three months after shock 

treatment.

3.1.1.3 Potential Water Quality Issues 

Regrowth of Legionella following superheat-and-flush has been identified as an issue (Stout and 

Yu, 2003). Recolonization could be caused by the survival properties of Legionella spp. (i.e., the 

ability to colonize biofilms, ability to parasitize and multiply within protozoa, and ability to enter 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 52 October 2015 

a VBNC state, as discussed in Section 1.2.3), or failure to properly address the conditions that 

caused the problem (such as dead ends, stagnation and low flow). Researchers have revealed that 

Legionella can rapidly proliferate after temperatures are lowered, presumably via microbial 

response to the nutrients released by the newly killed biofilm (necrotrophy) (Temmerman et al., 

2006). This finding indicates that disturbing the microbial ecology on a short-term basis may 

exacerbate pathogen regrowth in the long-term (Pruden et al., 2013). 

The superheat-and-flush method generally does not require special equipment; however, it is 

labor-intensive and time-consuming due to the need to monitor hot water temperature and 

flushing time. Several limitations of the superheat-and-flush method need to be recognized: 

• Superheat-and-flush is only applicable to hot water systems with sufficient heat capacity. 

It may be ineffective when parts of the boiler/water heater or the water system fail to 

reach the required temperature (Lin et al., 2000a) or in systems that do not have hot water 

lines to every distal site. 

• Superheat-and-flush requires considerable energy and manpower resources. 

• Thermal disinfection will not disinfect downstream of thermostatic mixer valves and so is 

of limited value where such valves are installed (HSE, 2009). 

• Scalding is a significant hazard (Rosenblatt and McCoy, 2014). Caution must be taken 

during emergency disinfection to avoid potential scalding. 

• The high temperature employed in this method can damage pipes and may cause failure 

of elastomeric seals, resulting in pump failure and leakage across valves (Rosenblatt and 

McCoy, 2014). Pipe material should be assessed before considering this approach. 

3.1.1.4 Operational Conditions 

Recommendations for conducting an effective superheat-and-flush, based on the published 

standards and guidelines (HSE, 2014; Department of Veterans Affairs, 2014; ASHRAE, 2015; 

HSE, 2009; CDC, 2003; ASHRAE, 2000), are summarized as follows: 

• When possible, perform flushing when the fewest building occupants are present (e.g., 

nights and weekends). 

• Post signage and warning notices at all areas of the building to alert occupants of the 

potential scalding hazard.

• Maintain water heater temperatures at 71–77 degrees C (160–170 degrees F) while 

progressively flushing each outlet in the system for up to 30 minutes at 65 degrees C (149 

degrees F). 

• Flushing multiple outlets simultaneously can save time, but should not exceed the 

capacity of the water heater and the flow capacity of the system.

• Perform flushing in a manner that reduces the risk of scalding and aerosolization of 

potable water in patient-care areas. 

• Following superheat-and-flush treatment, maintain hot water system temperature >60 

degrees C (140 degrees F) in all hot water lines. 

• At the end of the procedure, collect samples of water at distal outlets of the water system. 

After the water temperature has returned to normal, Legionella culture should be done to 

determine efficacy of the treatment. Culture should be repeated within two weeks of 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 53 October 2015 

treatment to determine if there is any short-term control. Repeat the procedure until 

decontamination is achieved. Following decontamination, microbiological checks must 

be repeated periodically. 

3.1.2 Shock Hyperchlorination

3.1.2.1 Background 

Hyperchlorination involves injecting chlorine at an elevated concentration into the building 

water system in one of two modes: shock or continuous hyperchlorination. Shock 

hyperchlorination, often used for emergency disinfection, is the injection of chlorine to achieve a 

level of 20–50 mg/L of free chlorine (as chlorine) (HSE, 2014; Department of Veterans Affairs, 

2014). After a sufficient contact time, the water is flushed and the residual chlorine is returned to 

its normal level. Continuous hyperchlorination is accomplished by continuous injection of 

chlorine to achieve at least 0.5–1.0 mg/L (as chlorine) free chlorine (HSE, 2014). It is often 

performed as a post-emergency disinfection procedure to aid the control of Legionella and 

biofilms. Continuous hyperchlorination in building water systems is discussed in Section 2.3.1. 

3.1.2.2 Characterization of Effectiveness Against Legionella 

Hyperchlorination can be applied to the cold- and hot-water tanks and to the entire building 

water system. It may be the only option in some healthcare facilities where superheat-and-flush 

cannot be used because hot water lines are not available at every distal site or they cannot reach 

the required high temperature.

The success of hyperchlorination in the control of Legionella has been mixed, as shown in the 

case studies below and other studies in Section 2.3.1: 

• Grosserode et al. (1993) reported a 10-year follow-up study of the efficacy and 

environmental effects of hyperchlorination for control of nosocomial legionellosis at a 

university hospital. In the 10 years following an outbreak in 1981, the incidence fell 

dramatically from 35 to less than 1 per 1,000 admissions; the frequency of cases of 

legionellosis also declined significantly from 16 cases among 21 tested to 5 cases among 

294 tested. No Legionella spp. were isolated from the more than 500 water samples 

collected during the 10-year period. 

• García et al. (2008) conducted long-term surveillance and studied the persistence of 

Legionella in finished water systems at a hospital and a hotel before and after multiple 

hyperchlorination treatments. Each facility had been associated with cases of 

Legionnaires’ disease. Prior to May 1998, the hotel’s finished water system was 

interconnected with the industrial water system. Over the period August 1992 to April 

2001, at least seven hyperchlorination treatments were applied using a dosage rate of 10 

ppm and contact time of five hours, or a dosage rate of 20 ppm and contact time of eight 

hours. Between 1984 and 1995, the hospital’s water system was treated with 

hyperchlorination four times (dosage rate and contact time not stated by authors). 

Environmental monitoring after each treatment showed that Legionella was absent for a 

period of a few months. New cases of Legionnaires’ disease also occurred after 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 54 October 2015 

hyperchlorination. The results of Legionella sampling also demonstrated that successive 

hyperchlorination treatments did not modify the susceptibility of bacteria to new 

treatments with chlorine or other disinfectants. The authors noted that interaction with 

other microorganisms, such as amoebae, could favor the persistence of Legionella, as 

noted in a previous investigation by Kilvington and Price (1990). 

• Despite shock hyperchlorination (with 50 mg/L) being applied to the cold- and hot-water 

tanks and to the whole building water system, Legionella colonization persisted in a 250-

bed hospital (Biurrun et al., 1999). A continuous chlorine system was installed in the 

cold-water tanks to achieve approximately 0.8 mg/L of free residual chlorine at the coldwater outlets (higher levels of chlorine and thermal treatment were not desired due to the 

poor condition of the piping). This, along with elimination of dead ends, replacement of 

contaminated fixtures, and other corrective measures, reduced the number of positive 

sample sites from 88 percent to 17 percent. But one month later, colonization was 

detected at a positive rate of 58 percent. 

• A study of 62 hotels in Spain evaluated the use of continuous chlorination at 1–2 mg/L of 

free residual chlorine in the cold water, combined with intermittent thermal treatment in 

the hot water. Samples positive for Legionella dropped from approximately 30 percent 

after the first year of application, to 20 percent after three years, and to 6 percent after 

five years (Crespi and Ferra, 1998).

In general, the efficacy of shock hyperchlorination is affected by the same factors as continuous 

hyperchlorination, as described in Section 2.3.1. Shock hyperchlorination, if conducted alone, 

would not achieve long-term control of Legionella. Researchers reported that Legionella could 

be protected within free-living protozoan cysts of Acanthamoebae, which can survive free 

chlorine concentrations up to 50 mg/L, the same concentration used in shock hyperchlorination 

(Storey et al., 2004a; Kilvington and Price, 1990). 

3.1.2.3 Potential Water Quality Issues 

Regrowth of Legionella may occur within days or weeks after shock hyperchlorination is 

discontinued (Cooper and Hanlon, 2009), just as with the superheat-and-flush method. Multiple 

shock hyperchlorination treatments may be needed in response to positive potable water cultures, 

followed by continuous hyperchlorination or other treatment measures to achieve long-term 

results.

Caution must be taken during shock hyperchlorination to avoid exposures to high disinfectant 

levels. Signs and warning labels should be posted at sinks and other outlets to warn building 

occupants not to use the water (HSE, 2014). When possible, shock hyperchlorination should be 

performed when the fewest building occupants are present (e.g., nights and weekends). 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 55 October 2015 

3.1.2.4 Operational Conditions 

Recommendations for conducting effective shock hyperchlorination, based on published 

guidelines (HSE, 2014; HSE, 2009; ASHRAE, 2000; Grosserode et al., 1993), are summarized 

below: 

Shock hyperchlorination of hot and cold water systems can significantly impact the physical 

integrity of the piping system and water fixtures if applied incorrectly or too often. Corrosion of 

metal pipes and appurtenances may occur from exposure to high levels of free chlorine (CDC, 

2003). Therefore, routinely performing these procedures is not recommended (HSE, 2014). 

Other recommendations include the following: 

• Post signage and warning notices at all areas of the building to alert occupants of the 

potential chemical hazard.

• When possible, shut off and bypass any existing water treatment equipment (e.g., water 

softeners, carbon filters).

• Clean the tanks and associated fittings. Remove sediment, sludge and stagnant water. 

Correct other problems that may harbor Legionella. Rubbers containing thiuram disulfide 

do not enhance the growth of Legionella, and some have suggested the use of such rubber 

in water systems (Niedeveld et al., 1986). 

• To prevent colonization from recurring after emergency disinfection is discontinued, the 

initial conditions that caused the problem (such as stagnation and low flow) need to be 

identified and corrected; the water temperature needs to be maintained at a proper level 

(>60 degrees C, or 140 degrees F); or a residual disinfection treatment needs to be 

installed for long-term routine operation. 

• Consider the use of continuous hyperchlorination, or other form of long-term treatment, if 

cases continue to be identified or if a Legionella strain isolated from patients persists in 

the building water system. If Legionella isolates are limited to the hot water system, 

continuous hyperchlorination should be initiated for the hot water system alone. Chlorine 

levels need to be adjusted as required to keep DBPs at acceptable levels. 

• Monitor the hyperchlorinated building water system for pipe damage. Assays for levels 

of copper, lead and iron, along with use of corrosion and water stability indexes, may 

permit early detection and control of corrosion problems. 

3.2 Point-of-Use Filtration

3.2.1 Background 

POU filtration is defined as the use of a device applied to a single tap for the purpose of reducing 

contaminants in drinking water at that one tap. POU filtration can be used at specific taps, 

faucets and showerheads as a temporary measure to provide a physical barrier against 

Legionella. Hospitals have used this technology to try to reduce disease transmission (Ortolano 

et al., 2005). POU water filtration may be an effective measure for remediation situations if a 

limited patient area can be targeted. Filters can be installed immediately and are a better 

alternative than restricting showering and providing bottled water. 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 56 October 2015 

Advances in membrane filter technology have resulted in POU filtration systems capable of 

removing microorganisms (USEPA, 2005b; USEPA, 2001). These treatment systems include 

microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) 

processes. MF and UF use hollow-fiber membrane material contained in cartridges which 

separate particles using a sieving mechanism based on the pore size and particle size. NF and RO 

use spiral-wound (consisting of a flat sheet of membrane material wrapped around a central 

collection tube) filter elements or cartridges. They are semi-permeable membranes without 

definable pores. NF and RO are both pressure-driven systems that function similarly in their 

removal mechanisms for microbial contaminants. Exhibit 3-1 describes the average pore size and 

molecular weight cut-off requirements for different membrane filtration devices. For 

comparison, Legionella cells are typically 0.3–0.9 micrometers (μm) wide and 2–20 μm long 

when grown in laboratory culture (Bartram et al., 2007). 

Exhibit 3-1: Membrane filtration guide for removal of microbial contaminants

Source: USEPA, 2005b. 

EPA defines two criteria for membrane filtration technology for pathogen removal under the 

Safe Drinking Water Act’s (SDWA) Long Term 2 Enhanced Surface Water Treatment Rule (40 

CFR 141.2):

• The filtration system must be a pressure- or vacuum-driven process and remove 

particulate matter larger than 1 μm (for Cryptosporidium, specifically) using an 

engineered barrier, primarily via a size exclusion mechanism.

• The process must have a measurable removal efficiency for a target organism that can be 

verified through the application of a direct integrity test.

Nominal Pore Size (microns) 

 0.0001 0.001 0.01 0.1 1.0 10 100

Molecular Weight 

(daltons)

 200 20,000 200,000

Microbial 

Contaminants

 

 Cryptosporidium

Membrane 

Filtration Process

 Bacteria

 Giardia

 

 Viruses

 MF

 UF

 NF

 RO
Draft – Technologies for Legionella Control: 

Scientific Literature Review 57 October 2015 

Many homeowners; building owners; and operators of hospitals, nursing homes, and hotels 

utilize POU membrane filtration devices, often in a proactive manner but also in response to 

emergencies (USEPA 2006d). Some hospitals use POU membrane filtration treatment in areas 

populated with high-risk patients (e.g., in oncology, bone marrow and solid organ transplant, and 

ICUs). 

Two ANSI standards exist for certification of POU devices used for removal of microbial 

contaminants: Standard 53 (Drinking Water Treatment Units - Health Effects) and Standard 58 

(Reverse Osmosis Drinking Water Treatment Systems). POU filtration devices have been 

certified by NSF International for removal of protozoa, bacteria and viruses in general, using 

surrogate microorganisms as challenge organisms during testing and evaluation. Lists of POU 

devices certified by independent, accredited laboratories to meet these standards are available 

from Underwriters Laboratories (www.ul.com), NSF International (www.nsf.org/certified/dwtu), 

and the Water Quality Association (www.wqa.org). Note that although some POU filtration 

devices have been certified to meet bacterial removal standards, they have not been certified 

specifically for removal of Legionella. 

3.2.2 Characterization of Effectiveness against Legionella 

Several case studies describe the effectiveness of POU membrane filtration devices for removal 

of Legionella. 

• Casini et al. (2014) reported the efficacy of POU filtration installed in selected wards of 

an Italian hospital to further reduce Legionella growth within the building hot water 

system after chloride dioxide disinfection. POU filters used in this study had a 0.2-μm 

nominal pore size and 30-day replacement rate. This integrated disinfection-filtration 

strategy, although expensive, significantly reduced Legionella counts to less than 103

CFU/L and achieved a positive sample rate of less than 30 percent. 

• Baron et al. (2014) evaluated a new faucet filter at five sinks in a cancer center and found 

that Legionella was removed from all filtered samples for 12 weeks, exceeding the 

manufacturer's recommended maximum duration of use of 62 days. The filters contain a 

30-μm pre-filtration layer, a 1-μm membrane and a 0.2-μm membrane.

• Marchesi et al. (2011) performed a 10-year review of multiple treatment methods to 

control for Legionella at a hospital in Italy, including POU filtration, though information 

on the characteristics of the filters was not supplied. Filters were placed in high-risk units 

of the hospital only, where high levels of Legionella contamination were identified, and 

were replaced every 30 days. No Legionella were detected at taps containing POU filters. 

• Daeschlein et al. (2007) evaluated a reusable POU filter for removing waterborne 

pathogens, including L. pneumophila, in a hospital’s transplant unit for eight weeks. 

Filters had three configurations: (1) hollow fiber of polyethersulfone with pore size 0.2 

μm and surface area of 800 cm2

; (2) hollow fiber of polyethersulfone with pore size 0.2 

μm, surface area of 1100 cm2

, and inner encasement coated with nanosilver; and (3) same 

as (2) with metallic silver outlet.
Draft – Technologies for Legionella Control: 

Scientific Literature Review 58 October 2015 

Filters were placed on 18 taps (12 taps, six showers) in the hospital’s transplant unit and 

each filter was monitored for pathogens at one, four and eight weeks, reprocessed and reused in three additional trials. Over the test period, no Legionella or other pathogens were 

detected in any filter effluent. Because bacterial counts in filtered water exceeded the 

limit of >100 CFU/mL eight times, the following criteria were developed to prevent 

carry-over contamination from re-use of the filters: filters were cleaned with a strong 

chemical followed by flushing and thermal disinfection in a quality control-compliant 

washer-disinfector once a week, in addition to alcohol disinfection of the filter 

encasement. With this reprocessing, the authors determined that filters should be changed 

after four weeks in high-risk areas and after eight weeks in moderate-risk areas.

• A newer version of the filters described in the example by Daeschlein et al. (2007) was 

evaluated by Vonberg et al. (2008) at a hospital in Germany. The new version had a 

membrane surface coated with nanosilver. Fifteen taps in a thoracic surgery department 

were selected and sampled before adding filters. Filters were placed on those taps and 

sampled after one, two, three and four weeks of usage. Samples were analyzed for the 

pathogens Legionella and Pseudomonas, in addition to the indicators enterococci and 

heterotrophic bacteria. Legionella were detected in nearly half (48.3 percent) of taps 

before filters were added and only one sample (week 1) after filters were added (L. 

pneumophila serogroup 1, 4 CFU/mL); no Pseudomonas were detected. The authors did 

not attempt to reprocess the filters as in the Daeschlein study and did see heterotrophs 

increase to >100 CFU/mL in some filters after one week of use. The authors concluded 

that incorporation of nanosilver in the filter’s membrane surface coating may prevent 

biofilm growth in this POU device and that use of these POU filters with weekly 

replacement in high-risk patient wards may be effective at preventing nosocomial 

legionellosis. 

• Sheffer et al. (2005) evaluated POU filtration devices containing positively charged nylon 

membranes with a 0.2-μm nominal pore size. Filters were placed on four taps in the 

administration building at a hospital and monitored for Legionella, heterotrophic bacteria, 

and mycobacteria, along with three taps without filters, every 2–3 days for 13 days, 

before and after a one-minute flush. Samples from taps with filters before flush were 

negative for Legionella during the 13-day period, while mean concentration in taps 

without filters was 104.5 CFU/mL. Mycobacterium gordonae was isolated from 10.3 

percent of taps without filters before flushing, but no mycobacteria were isolated from 

taps with filters before flushing. Heterotrophs were significantly reduced at taps with 

filters. One post-flush sample from a tap with a filter was positive for Legionella on day 

10 with a concentration of 5 CFU/mL. No post-flush samples from taps with or without 

filters were positive for mycobacteria. The authors concluded that the POU filters used in 

this study effectively eliminated Legionella and mycobacteria through seven days of use 

and yielded a >99 percent reduction in heterotrophic bacteria.

• Molloy et al. (2008) evaluated three types of POU solid block activated carbon filters for 

removal of L. pneumophila in a laboratory-simulated domestic water system: (1) carbon 

containing copper, (2) carbon containing copper and silver, and (3) carbon without 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 59 October 2015 

metals. Filters were challenged with tap water seeded with L. pneumophila multiple times 

and water was monitored under simulated domestic use for six weeks. Levels of 

Legionella were reduced by all three filters by nearly 8 log, but they were detected in all 

filter effluents for the length of the study. The authors concluded that the organisms 

attached to the carbon blocks and sloughed off over time. 

3.2.3 Potential Water Quality Issues 

POU filters have the potential to concentrate bacteria and foster growth of pathogens. Failure of 

filters could lead to the release of high levels of pathogens. Membranes may foul, clog with scale 

(from salts in feed water), or be degraded by microorganisms. 

3.2.4 Operational Conditions

In general, most POU devices include pre-filtration (usually granular activated carbon) to treat 

inlet water and prevent clogging of the central membrane, the central filtration membrane, and 

post-filtration, in a module configuration. Design guidance for POU filtration devices can be 

found in the EPA’s Membrane Filtration Guidance Manual (USEPA, 2005b). Operators are 

advised to follow the manufacturer’s operational guidance for the POU system being employed. 

There is a variety of commercially available systems with unique design features and operational 

conditions. Additional guidance on operation and maintenance for POU treatment devices, 

including examples of maintenance logs, can be found in EPA’s POU or POE Treatment 

Options for Small Drinking Water Systems (USEPA, 2006d). A detailed maintenance log should 

be kept for each system, based on the state’s requirements, if any. Maintenance typically 

includes the following: 

• Tracking flows - Flow meters are used to measure the total flow treated, as flow values 

may be used to determine filter membrane or other component replacement parameters.

• Replacement parts - Components should be replaced as required by the manufacturer or 

monitoring data, to ensure water free of microbial contaminants. Minimal components 

needing regular replacement include exhausted membranes and pre- and post-filters. A 

30-day replacement rate was reported in the studies using POU filters for Legionella

control in hospitals (Casini et al., 2014; Marchesi et al., 2011). 

• Visual check of mechanical conditions - All components, including the mechanical 

warning device, should be inspected visually on a regular basis and parts 

replaced/repaired if necessary, in addition to being replaced as specified by the routine 

replacement schedule. 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 60 October 2015 

4 Questions and Answers on Legionella Control in Building Water Systems

4.1 Public Health Concerns

Q1. What are the threats from Legionella in a building water system?

Legionella is a naturally occurring bacterial pathogen that can be present in municipal and other 

water supplies. Building water systems may provide conditions (e.g., low flow/long retention 

times, optimal temperature, and low disinfectant residual levels) that favor its growth to levels 

that may result in increased risk to public health (i.e., developing legionellosis). For more details 

please see Section 1.2 of this document. 

Q2: Do all species of Legionella cause disease?

Although most of the diagnosed cases of legionellosis (Legionnaires’ disease and Pontiac fever) 

are associated with Legionella pneumophila (serogroup 1), approximately half of all the species

of Legionella have been associated with clinical cases of legionellosis. However, it is likely that 

most Legionellae can cause human disease under the appropriate conditions (e.g., in individuals 

in higher risk groups) (Borella et al., 2005; Fields, 1996; Fang et al., 1989). For additional 

information, please see Section 1.2 of this document. 

Q3. Do you need to eliminate all Legionellae in order to have a safe building environment?

Not necessarily. Due to the highly variable and inconclusive information that is available, it is 

not feasible to establish a definitive action level below which the risk from disease is eliminated. 

Building water system operators may choose to assess the population they serve for individual 

factors that may increase the risk of disease (e.g., age, immunosuppression) to reduce the risks 

from Legionellae. See Section 1.2.2 for additional information on risk factors. The building 

water operator and/or manager may want to evaluate the building water system processes that 

could contribute to Legionella growth (e.g., long hot water holding times). This assessment 

should allow the building water system manager to determine the necessary stringency of the 

control plan and measures (see Section 2.2 for additional information).

4.2 Potential Regulatory Requirements 

Q4. What constitutes being a regulated public water system?

The criteria for being a regulated public water system (PWS) are codified at 40 CFR 141.3. 

Where there are questions about the application of these criteria, the primacy agency (typically 

the state) will make the determination based on these criteria and any relevant site-specific 

considerations. 

Q5. Will a building that installs a treatment specifically designed for Legionella and serves 

a population above the threshold of a PWS definition be subject to SDWA requirements?

See response to Question 4. 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 61 October 2015 

Q6. Why do I need to comply with drinking water standards if I’m only treating the hot 

water (not for drinking purposes)?

EPA considers water for human consumption to include water for drinking and food preparation 

as well as water for brushing teeth, showering and hand washing (See 63 FR 41940; August 5, 

1998). 

Q7. If I comply with the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA) 

pesticide registration requirements, am I in compliance with the Safe Drinking Water Act 

(SDWA) requirements?

The pesticide registration requirements under FIFRA are independent of the SDWA 

requirements, and each mandate targets complementary, yet different, environmental and public 

health protection objectives. Registration of a pesticide product under FIFRA does not mean that 

it meets the requirements of other environmental and public health protection statutes, including 

the SDWA or vice versa.

The objective of FIFRA is to protect human health and the environment through federal control 

of pesticide distribution, sale and use. All pesticides distributed or sold in the United States must 

be registered (licensed) by EPA. Registration assures that pesticides are properly labeled and 

that, if used in accordance with their approved labeling, they will not cause unreasonable adverse 

effects on the environment or human health. 

Registration is required for pesticide products that are sold or distributed in the United States for 

antimicrobial applications. However, this requirement does not necessarily preclude the use of 

other disinfectants recognized under the Surface Water Treatment Rules such as chlorine, 

chlorine dioxide and chloramines.

The SDWA is the main federal law that ensures the quality of Americans' drinking water. Under 

SDWA, EPA sets standards for drinking water quality and oversees the states, localities and 

water suppliers who implement those standards. 

While there are no requirements under SDWA that prohibit the installation of a given 

technology, the primacy agency is responsible for accepting the installation or usage of new 

technologies in PWSs. Both SDWA and FIFRA allow states to have stricter standards than those 

prescribed in federal regulations. This includes the authority to request additional data or 

information before approving a drinking water treatment technology or pesticides (see response 

to Question 8 for additional information) to be used within the state. In the case of a pesticide, a 

state can require compliance with a state-specific pesticide registration process in addition to the 

EPA registration. With regard to technologies for drinking water treatment, primacy agencies 

and technology manufacturers can refer to EPA’s Water Supply Guidance (WSG) 90 for 

guidance on some of the types of data or information that may be requested as part of the 

primacy agency’s evaluation and approval of alternative drinking water treatment technologies.

Q8. What are the pesticide registration requirements related to pesticide products and 

devices for the control of Legionella (and other microbial contaminants)?

Pesticide products and devices that make antimicrobial claims of efficacy against L. 

pneumophila are subject to certain EPA regulatory requirements. FIFRA defines a pesticide as 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 62 October 2015 

any substance or mixture of substances intended for preventing, destroying, repelling or 

mitigating any pest. The term pesticide includes antimicrobials (e.g., sanitizers and disinfectants) 

in addition to various other substances used to control pests. Products that contain a substance or 

mixture of substances and that make a pesticidal claim must be registered by EPA prior to sale or 

distribution. For products that claim efficacy against a public health pest, an applicant must 

submit data demonstrating that efficacy to obtain a registration. 

While devices are subject to certain EPA regulatory requirements, they do not require 

registration as pesticide products. A pesticide device is defined in FIFRA as an instrument or 

contrivance (without a chemical substance) that is used to destroy, repel, trap or mitigate any

pest such as insects, weeds, rodents, animals, birds, mold/mildew, bacteria and viruses. A device 

is subject to the FIFRA prohibition against misbranding and must be produced in an EPAregistered establishment. To be considered a device, the item must not be sold or distributed with

a substance or mixture of substances to perform its intended pesticidal purpose. For example,

drinking water treatment technologies that incorporate a substance (e.g., chlorine, chloramine, 

silver or copper in the form of an electrode) for pesticidal purposes are not considered to be 

pesticide devices and must be registered. Additional information on pesticide devices and the 

associated FIFRA requirements is available on EPA’s website and includes fact sheets and a 

registration manual. For additional information regarding obtaining installation or operating 

permits see response to Question 20.

4.3 Control Measures

Q9. What measures can a building operator take to control the colonization and 

amplification of Legionella in a building water system? 

Buildings can vary in their characteristics (e.g., dimensions, location with respect to the servicing 

PWS) as well as their purposes. The appropriate treatment depends on those characteristics and 

purposes. A multi-barrier approach can be used to ensure a comprehensive preventative approach 

is taken to address potential health risks related to the building water system. See Section 2.2 of 

this document for information on multi-barrier approaches.

Q10. Does EPA regulate Legionella? 

EPA regulates Legionella under the Surface Water Treatment Rule (SWTR). The SWTR has 

treatment technique requirements to control for Giardia and viruses. The SWTR assumes that if 

sufficient treatment is provided to control for Giardia and viruses (i.e., 3-log inactivation of 

Giardia and 4-log inactivation of viruses), then Legionella should be addressed as well. In 

addition, the Revised Total Coliform Rule and the Ground Water Rule have treatment technique 

requirements that address bacteria, which provide some control of Legionella. All of these rules 

apply to PWSs. They would not apply to building water systems unless the facility is a regulated 

PWS. See response to Question 4. 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 63 October 2015 

Q11. What treatment technologies does EPA approve for control of Legionella in drinking 

water?

EPA does not approve any treatment technologies specifically for control of Legionella in 

drinking water. See response to Question 17. 

Q12. What is supplemental disinfection?

For the purposes of this document, supplemental disinfection refers to any additional treatment 

added, such as that added to reduce Legionella, to supplement or boost the treatment provided by 

the distributor of the water being received. To address water quality and pathogen control needs, 

building operators and owners, after a careful review of building and water system conditions, 

may wish to implement a supplemental application of a disinfectant specific to and within the 

building water system. Supplemental treatment in this case does not refer to emergency 

disinfection by the building owner or operator (i.e., water disinfected as a result of the 

emergency that is not intended for human consumption). 

Q13. What happens if I add supplemental disinfection in my building? 

You will need to determine whether the application of that treatment triggers additional SDWA 

requirements, for example, requiring the building water system to be fully regulated as a PWS. 

You may wish to consult with your water supplier (i.e., PWS) to better understand any potential 

water quality issues before making treatment-related decisions. If a decision to add treatment to 

the building water system seems likely, EPA advises building owners to consult with their 

primacy agency to determine if any SDWA requirements apply; in addition, there may be state or 

local requirements that apply to the treatment or the water system. See Section 1.4 for additional 

information. 

Q14. What should I do before I consider supplemental water treatment?

Building owners and operators considering the addition of a supplemental water treatment 

system are encouraged to contact their primacy agency and other state and local authorities and 

familiarize themselves with applicable federal, state and local regulations (e.g., building codes, 

local health codes). Building owners and operators should also become very familiar with the 

characteristics and needs of their system to help determine the most appropriate supplemental 

water treatment. Please see Section 2.3 of this document for more information on treatment 

technologies that could be used as supplemental treatment. 

Q15. Are there any advantages to supplemental disinfection?

Facilities that design, operate, control and monitor supplemental treatment systems ensure that a 

high level of water quality is maintained, improving public health protection and reducing 

liabilities. Providing supplemental disinfection can help maintain the high level of water quality 

throughout the building water system. 

Q16. Are there any disadvantages to supplemental disinfection?

Operating supplemental water treatment requires the commitment of financial, physical and staff

resources. An additional disadvantage is that installation of supplemental treatment could lead to 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 64 October 2015 

a false sense of security. Installation of supplemental disinfection does not negate the need for 

building owners/customers to respond to water supply emergencies (i.e., boil water advisories, 

“do not consume” notices, “do not use” notices) issued by the selling system.

4.4 New Technology Approval 

Q17. What is EPA’s process for approval of new treatment technologies to control 

Legionella in drinking water?

Rather than approve new treatment technologies, EPA recognizes them for their capacity to 

achieve treatment technique requirements for control of pathogens (under rules such as the 

SWTR, GWR and LT2ESWTR). The EPA defers to the primacy agency for the approval of 

technologies that PWSs can use to comply with treatment technique regulations. The EPA, in 

cooperation with the Association of State Drinking Water Administrators, state drinking water 

program personnel, industry representatives, and other stakeholders, developed a Water Supply 

Guidance document (WSG 90) that provides a streamlined protocol to facilitate consistent state 

approvals of new drinking water treatment technologies. WSG 90 is not meant to replace current 

state plan review and approval processes. Note that new technologies may need to comply with 

registration or other requirements for pesticide products and devices under FIFRA (See response 

to Question 8). 

Q18. How do states approve new treatment technologies for Legionella control? 

Many states utilize a plan approval or permitting process to approve the installation of treatment 

at PWSs. For new treatment technologies, many states (47) require conformance to ANSI/NSF 

Standard 60 and/or 61. In addition, states may require third-party validation of efficacy. States 

may also use the protocol described in WSG 90 to facilitate consistent state approvals of new 

drinking water treatment technologies. WSG 90 is not meant to replace current state plan review 

and approval processes. 

If you are planning to install additional treatment in your building/facility, consult with your 

primacy agency regarding any additional specific requirements. If you require further assistance, 

contact the appropriate EPA regional office for additional information. For additional 

information, please refer to Question 30 (Additional Sources of Information). 

4.5 Permitting 

Q19. What is the procedure for plan review and permitting to operate a Legionella

treatment system?

The procedure for plan review and approval or permitting varies from state to state. Some states 

require a permit to construct/install a treatment system and a separate permit to operate the 

system. Water system owners should consult with their water provider and primacy agency to 

find out specific procedures and requirements. Alternatively, contact the appropriate EPA 

regional office for additional information. 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 65 October 2015 

4.6 Sampling and Monitoring 

Q20. If I am only treating the hot water, where should I take compliance samples? 

SDWA requirements for PWSs apply to any water for human consumption regardless of the 

temperature of the water. Consult with your primacy agency regarding site-specific 

requirements. Alternatively, contact the appropriate EPA regional office for additional 

information. 

Q21. What type of sampling (based on the selected treatment) will I be required to do?

Consult with your primacy agency regarding applicable sampling requirements. Alternatively, 

contact the appropriate EPA regional office for additional information. 

Q22. What residual disinfectants and DBPs do I need to monitor? 

The Stage 1 DBPR and Stage 2 DBPR established MCLs for DBPs and MRDLs for disinfectant 

residuals. It also specified the monitoring requirements that PWSs must perform for residual 

disinfectants and DBPs (type, frequency and location), depending on the type of systems, 

population served and type of disinfectants being used. For example, a regulated PWS using 

chlorine or chloramine must monitor for TTHM, HAA5 and residual chlorine. A regulated PWS

using chlorine dioxide must monitor for TTHM, HAA5, chlorite and chlorine dioxide. See the 

Stage 2 DBPR Quick Reference Guide for more information.

Q23. How do I monitor for chlorine dioxide? 

For regulated PWSs, chlorine dioxide is a contaminant with acute health effects and must be 

monitored daily at the entry point to the distribution system and at each treatment unit location to 

ensure it is not exceeding the MRDL of 0.8 mg/L. Chlorine dioxide has a short sample hold time 

and must be measured immediately after collection; therefore, on-site analysis at the water 

system is required. 

The approved analytical methods for measuring residual disinfectant concentration for chlorine 

dioxide include Standard Method 4500-ClO2 D and E (40 CFR 141.131(c)). These methods 

indicate that systems may also measure residual disinfectant concentrations for chlorine dioxide 

by using DPD colorimetric test kits, and the person conducting the measurements must be 

approved by EPA or the state. 

Facilities considering installation of this technology should coordinate with the primacy agency 

to determine requirements for approval. Some primacy agencies are requiring the water systems’

staff members who are conducting on-site analysis of chlorine dioxide and chlorite to prove 

analytical competency by performing an initial demonstration of capability as well as an ongoing 

demonstration of capability. 

Q24. Can I send daily chlorite and chlorine dioxide samples to a lab? 

If you are subject to Stage 2 requirements, you are required to analyze daily chlorite samples onsite and send monthly chlorite samples to a certified laboratory (see table footnote 8 in 40 CFR 

141.131(b)). You cannot send daily chlorine dioxide samples to a laboratory for analysis because 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 66 October 2015 

chlorine dioxide has a short sample hold time and must be measured on-site immediately after 

collection. 

Q25. Does EPA require Legionella monitoring if treatment for its control is installed? If so, 

what are the targets for meeting control? 

No; EPA does not have requirements for Legionella monitoring. However, state or local agencies 

may specify such requirements in the permit conditions for the permit to operate issued to the 

facility. In addition, there may be requirements for monitoring of water quality parameters or 

treatment process parameters on a routine basis. 

Q26. If a facility has treatment and has either an outbreak or has Legionella test results 

showing detections, are they required to report to the primacy agency? 

If the facility is a regulated PWS, there will be reporting requirements defined by the state in 

response to a waterborne disease outbreak, Legionella detection, or even water quality conditions 

that may contribute to an outbreak. Facilities that are not PWSs might have to share information 

about an outbreak or Legionella detection with local health authorities. These agencies will be 

able to assist with response actions. 

4.7 Operator Certification

Q27. What is operator certification? 

Operator certification is a program that establishes minimum professional standards for the 

operation and maintenance of PWSs to help protect human health and the environment. In 1999, 

EPA issued operator certification program guidelines specifying minimum standards for 

certification and recertification of the operators of community and non-transient non-community 

PWSs. These guidelines are currently being implemented through state operator certification 

programs. While the specific requirements vary from state to state, the goal of all operator 

certification programs is to ensure that skilled professionals are overseeing the treatment and 

distribution of safe drinking water. Operator certification is an important step in promoting 

compliance with SDWA. More information on operator certification is available on EPA’s 

website.

Q28. Do I need to have a certified operator for this treatment system? 

If your facility is a regulated PWS, (see questions in Section 4.2 to determine if you are 

regulated), you may be required to have a certified operator for your treatment system. There are 

two general types of operator certification — one for treatment systems and one for distribution 

systems. Within each type, there are different levels of certification. Consult with your primacy 

agency to determine the type and level of certified operator required for your specific system. 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 67 October 2015 

4.8 Unintended Consequences 

Q29. What are some of the unintended consequences of installing additional treatment for 

Legionella? 

For unintended consequences related to specific treatment technique requirements, please see the 

specific treatment sections in this document. 

4.9 Additional Sources of Information 

Q30. How can I obtain additional information on each treatment method? 

For additional information on any remaining general questions you can contact: 

• Safe Drinking Water Hotline by phone or email at:

– (800) 426-4791

– hotline-sdwa@epa.gov
Draft – Technologies for Legionella Control: 

Scientific Literature Review 68 October 2015 

5 References

Addiss, D.G., J.P. Davis, M. LaVenture, P.J. Wand, M.A. Hutchinson, and R.M. McKinney.

1989. Community-acquired Legionnaires' disease associated with a cooling tower: evidence for 

longer-distance transport of Legionella pneumophila. American Journal of Epidemiology,

130(3): 557–568. 

Aieta, E.M. and J.D. Berg. 1986. A review of chlorine dioxide in drinking water treatment. 

Journal AWWA, 78(6): 62-72. 

Alaska DEC. 2014. Treatment – ultraviolet (UV) disinfection system checklist. Alaska 

Department of Environmental Conservation. Available online at: 

http://dec.alaska.gov/eh/dw/Engineering/Plan_rev_checklist.htm. 

Alleron, L., A. Khemiri, M. Koubar, C. Lacombe, L. Coquet, P. Cosette, T. Jouenne, and J. 

Frere. 2013. VBNC Legionella pneumophila cells are still able to produce virulence proteins. 

Water Research, 47(17): 6606-6617. 

American Society for Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). 2000. 

Guideline 12-2000. Minimizing the risk of legionellosis associated with building water systems.

American Society for Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). 2015. 

ANSI/ASHRAE Standard 188-2015 Legionellosis: Risk management for building water systems. 

American Water Works Association (AWWA). 2012. ANSI-AWWA Standard F110 - ultraviolet 

disinfection systems for drinking water. American Water Works Association, Denver, CO. 

American Water Works Association (AWWA). 2013. Manual M56. Nitrification Prevention and 

Control in Drinking Water. Second Edition. American Water Works Association, Denver CO. 

American Water Works Association (AWWA) Disinfection Systems Committee. 2008. 

Committee Report: Disinfection Survey, Part 1 – Recent Changes, Current Practices and Water 

Quality. Journal AWWA, 100(10): 76-90. 

Antopol, S.C. and P.D. Ellner. 1979. Susceptibility of Legionella pneumophila to ultraviolet 

radiation. Applied and Environmental Microbiology, 38(2): 347-348. 

Araya, M., B. Chen, L.M. Klevay, J.J. Strain, L. Johnson, P. Robson, W. Shi, F. Nielsen, H. Zhu, 

M. Olivares, F. Pizzarro, and L.T. Haber. 2003a. Confirmation of an acute no-observed-adverseeffect and low-observed-adverse-effect level for copper in bottled drinking water in a multi-site 

international study. Regulatory Toxicology and Pharmacology, 38(3):389–399. 

Araya, M., M.C. McGoldrick, L.M. Klevay, J.J. Strain, P. Robson, F. Nielsen, M. Olivares, F. 

Pizarro, L. Johnson, and K.A. Poirier. 2001. Determination of an acute no-observed-adverseeffect level (NOAEL) for copper in water. Regulatory Toxicology and Pharmacology,

34(2):137–145. 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 69 October 2015 

Araya, M., M. Olivares, F. Pizarro, M. Gonzalez, H. Speisky, and R. Uauy. 2003b. 

Gastrointestinal symptoms and blood indicators of copper load in apparently healthy adults 

undergoing controlled copper exposure. American Journal of Clinical Nutrition, 77(3):646–650. 

Araya, M., M. Olivares, F. Pizarro, A. Llanos, G. Figueroa, and R. Uauy. 2004. Communitybased randomized double-blind study of gastrointestinal effects and copper exposure in drinking 

water. Environmental Health Perspectives, 112(10):1068–1073. 

Araya, M., C. Peña, F. Pizarro, and M. Olivares. 2003c. Gastric response to acute copper 

exposure. The Science of the Total Environment, 303(3):253–257. 

Armon, R., J. Starosvetzky, T. Arbel, and M. Green. 1997. Survival of Legionella pneumophila

and Salmonella typhimurium in biofilm systems. Water Science & Technology, 35(11-12): 293-

300. 

Baron, J.L., T. Peters, R. Shafer, B. MacMurray, and J.E. Stout. 2014. Field evaluation of a new 

point-of-use faucet filter for preventing exposure to Legionella and other waterborne pathogens 

in health care facilities. Amer. Journal of Infection Control, 42(2014):1193-1196. 

Baron, J. L., A. Vikram, S. Duda, J. E. Stout, and K. Bibby. 2014. Shift in the microbial ecology 

of a hospital hot water system following the introduction of an on-site monochloramine 

disinfection system. PLOS ONE. 9(7).

Barrette, W.C., D.M. Hannum, W.D. Wheeler, and J.K. Hurst. 1989. General mechanism for the 

bacterial toxicity of hypochlorous acid: Abolition of ATP production. Biochemistry, 28: 9172-

9178. 

Bartram, J., Y. Chartier, J.V. Lee, K. Pond, and S. Surman-Lee. 2007. Legionella and the 

prevention of legionellosis. 1st edition, World Health Organization, Geneva, Switzerland. 

Berg, J.D., J.C. Hoff, P.V. Roberts, and A. Matin. 1988. Resistance of bacterial subpopulations 

to disinfection by chlorine dioxide. Journal AWWA, 80(9): 115-119. 

Berger, T.J., J.A. Spadaro, S.E. Chapin, and R.O. Becker. 1976. Electrically generated silver 

ions: quantitative effects on bacterial and mammalian cells. Antimicrobial Agents and 

Chemotherapy, 9(2): 357-358. 

Berk, S.G., R.S. Ting, G.W. Turner, and R.J. Ashburn. 1998. Production of respirable vesicles 

containing live Legionella pneumophila cells by two Acanthamoeba spp. Applied and 

Environmental Microbiology. 64: 279-286. 

Best, M., V.L. Yu, J.E. Stout, R.R. Muder, A. Goetz, and F. Taylor. 1983. Legionella in the 

hospital water supply: Epidemiologic link with disease and evaluation of a method of control of 

nosocomial Legionnaires’ disease and Pittsburgh pneumonia. Lancet, 2: 307-310. 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 70 October 2015 

Biurrun, A., L. Caballero, C. Pelaz, E. León, A. Gago, 1999. Treatment of a Legionella 

pneumophila-colonized water distribution system using copper-silver ionization and continuous 

chlorination. Infection Control and Hospital Epidemiology. 20(6): 426-428.

Blanc, D.S., P. Carrara, G. Zanetti, and P. Francioli. 2005. Water disinfection with ozone, copper 

and silver ions, and temperature increase to control Legionella: seven years of experience in a 

university teaching hospital. Hospital Infection, 60: 69-72. 

Blatt, S.P., M. D. Parkinson, E. Pace, P. Hoffman, D. Dolan, P. Lauderdale, R. Zajac, and G.P. 

Melcher. 1993. Nosocomial Legionnaires’ disease: aspiration as a primary mode of disease 

acquisition. The American Journal of Medicine, 95: 16-22. 

Boffardi, B.P. and J. Hannigan. 2013. A limited evaluation of pitting corrosion of copper piping 

in a hospital domestic hot water system using copper-silver ionization for Legionella control. The 

Analyst Technology Supplement, 4: 38-42. 

Bohach, G.A. and I. S. Snyder. 1983. Cyanobacterial stimulation of growth and oxygen uptake 

by Legionella pneumophila. Applied and Environmental Microbiology. 46(2): 528–531. 

Bollin, G.E., J.F. Plouffe, M.F. Para, and B. Hackman. 1985. Aerosols containing Legionella

pneumophila generated by shower heads and hot-water faucets. Applied and Environmental 

Microbiology, 50(5): 1128-1131. 

Bondarczuk, K. and Z. Piotrowska-Seget. 2013. Molecular basis of active copper resistance 

mechanisms in Gram-negative bacteria. Cell Biology Toxicology, 29: 397-405. 

Borella, P., E. Guerrieri, I. Marchesi, M. Bondi, and P. Messi. 2005. Water ecology of 

Legionella and protozoan: environmental and public health perspectives. Biotechnology Annual 

Review, 11: 355-380. 

Brieland, J., M. McClain, L. Heath, C. Chrisp, G. Huffnagle, M. LeGendre, M. Hurley, J. 

Fantone, and C. Engleberg. 1996. Coinoculation with Hartmannella vermiformis enhances 

replicative Legionella pneumophila lung infection in a murine model of Legionnaires' disease. 

Infection and Immunity, 64: 2449-2456. 

Buse, H.Y. and N.J. Ashbolt. 2011. Differential growth of Legionella pneumophila strains within 

a range of amoebae at various temperatures associated with in-premise plumbing. Letters in 

Applied Microbiology, 53: 217-224. 

Buse, H.Y. and N.J. Ashbolt. 2012. Counting Legionella cells within single amoeba host cells. 

Applied and Environmental Microbiology, 78(6): 2070-2072. 

Buse, H. Y., J. Lu, I. T. Struewing, N. J. Ashbolt. 2013. Preferential colonization and release of 

Legionella pneumophila from mature drinking water biofilms grown on copper versus 

unplasticized polyvinylchloride coupons. Int. J. Hyg. Environ. Health. doi 

10.1016/j.ijheh.2013.04.005 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 71 October 2015 

Buse, H.Y., M.E. Schoen and N.J. Ashbolt. 2012. Legionellae in engineered systems and use of 

quantitative microbial risk assessment to predict exposure. Water Research, 46: 921-933. 

Calomoris, J.J. and K. Christman. 1998. How does chlorine added to drinking water kill bacteria 

and other harmful organisms? Why doesn’t it harm us? Scientific American. Available online at: 

http://www.scientificamerican.com/article/how-does-chlorine-added-t-1998-05-04/. 

Carducci, A., M. Verani, and R. Battistini. 2010. Legionella in industrial cooling towers: 

monitoring and control strategies. Letters in Applied Microbiology, 50(1): 24-29. 

Carlson, B.H. and G.L. Amy, 2001. Ozone and Biofiltration Optimization for Multiple 

Objectives. Journal AWWA, 93:1:88. 

Casini, B., A. Buzzigoli, M.L. Cristina, A.M. Spagnolo, P. DelGiudice, S. Brusaferro, A. Poscia, 

U. Moscato, P. Valentini, A. Baggiani, and G. Privitera. 2014. Long-term effects of hospital 

water network disinfection on Legionella and other waterborne bacteria in an Italian University 

Hospital. Infection Control and Hospital Epidemiology, 35(3): 293-299. 

Centers for Disease Control and Prevention (CDC). 1997. Sustained transmission of nosocomial 

Legionnaires’ disease – Arizona and Ohio. Morbidity and Mortality Weekly Report (MMWR),

46(19): 416-421. 

Centers for Disease Control and Prevention (CDC). 2000. Legionnaires’ disease associated with 

potting soil – California, Oregon and Washington, May-June 2000. Morbidity and Mortality 

Weekly Report (MMWR). 49: 777-778. 

Centers for Disease Control and Prevention (CDC). 2003. Guidelines for environmental infection 

control in health-care facilities. Recommendations of CDC and the Healthcare Infection Control 

Practices Advisory Committee (HICPAC). Morbidity and Mortality Weekly Report (MMWR), 52 

(RR10): 1-42. 

Centers for Disease Control and Prevention (CDC). 2005. Legionellosis (Legionnaire's disease or 

Pontiac fever) case definition. Available online at: 

http://wwwn.cdc.gov/NNDSS/script/casedef.aspx?CondYrID=741&DatePub=1/1/2005%2012:0

0:00%20AM. 

Centers for Disease Control and Prevention (CDC). 2008. Surveillance for waterborne disease 

and outbreaks associated with drinking water and water not intended for drinking – United 

States, 2005-2006. Morbidity and Mortality Weekly Report Surveillance Summaries, 57: 39-62. 

Centers for Disease Control and Prevention (CDC). 2011. Legionellosis – United States, 2000-

2009. Morbidity and Mortality Weekly Report (MMWR), 60: 1083-1086. 

Centers for Disease Control and Prevention (CDC). 2012. Summary of Notifiable Diseases – 

United States, 2012. Morbidity and Mortality Weekly Report (MMWR), 61(53): 1-121. 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 72 October 2015 

Centers for Disease Control and Prevention (CDC). 2013a. Legionella (Legionnaires' disease and 

Pontiac fever). Available online at: http://www.cdc.gov/Legionella/index.htmL. 

Centers for Disease Control and Prevention (CDC). 2013b. Surveillance for waterborne disease 

outbreaks associated with drinking water and other non-recreational water — United States, 

2009–2010. Morbidity and Mortality Weekly Report Surveillance Summaries, 62(35): 714-720. 

Cervero-Aragó, S., R. Sommer, and R.M Araujo. 2014. Effect of UV irradiation (253.7 nm) on 

free Legionella and Legionella associated with its amoebae hosts. Water Research, 67 (2014): 

299-309. 

Chen, C.H., L.C. Lin, Y. J. Chang, C.E. Liu, M.S. Soon, and C.S. Huang. 2013. Efficacy of 

copper-silver ionization for controlling fungal colonization in water distribution systems. Water 

and Health, 11(2): 277-280. 

Chen, Y.S., Y.E. Lin, Y.C. Liu, W.K. Huang, H.Y. Shih, S.R. Wann, S.S. Lee, H.C. Tsai, C.H. 

Li, H.L. Chao, C.M. Ke, H.H. Lu, and C.L. Chang. 2008. Efficacy of point-of-entry coppersilver ionization system in eradicating Legionella pneumophila in a tropical tertiary care hospital: 

implications for hospitals contaminated with Legionella in both hot and cold water. Hospital 

Infection, 68: 152-158. 

Chen, Y.S., Y.C. Liu, S.S. Lee, H.C. Tsai, S.R. Wann, C.H. Kao, C.L. Chang, W.K. Huang, T.S. 

Huang, H.L. Chao, C.H. Li, C.M. Ke, and Y.S. Lin. 2005. Abbreviated duration of superheatand-rush and disinfection of taps for Legionella disinfection: lessons learned from failure. 

American Journal of Infection Control. 33(10): 606-610. 

Chord, F., P. Fascia, F. Mallaval, J. Cornillon, L. Roesch, B. Pozzetto, F. Grattard, P. Berthelot. 

2011. Chlorine dioxide for Legionella spp. disinfection: a danger for cross-linked polyethylene 

pipes? Hospital Infection, 78(3): 242-243. 

Cirillo, J.D., S.L. Cirillo, L. Yan, L.E. Bermudez, S. Falkow, and L.S. Tompkins. 1999. 

Intracellular growth in Acanthamoeba castellanii affects monocyte entry mechanisms and 

enhances virulence of Legionella pneumophila. Infection and Immunity, 67(9): 4427-4434.

Colbourne, J.S. and P.J. Dennis. 1989. The ecology and survival of Legionella pneumophila. 

Water and Environment. 3: 345-350. 

Collier, S.A., L.J. Stockman, L.A. Hicks, L.E. Garrison, F.J. Zhou, and M.J. Beach. 2012. Direct 

healthcare costs of selected diseases primarily or partially transmitted by water. Epidemiology 

and Infection, 140: 2003-2013. 

Cooper, I.R. and G.W. Hanlon. 2009. Resistance of Legionella pneumophila serotype 1 biofilms 

to chlorine-based disinfection. Journal of Hospital Infection, 74 (2010): 152-159. 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 73 October 2015 

Craun, G.F., J.M. Brunkard, J.S. Yoder, V.A. Roberts, J. Carpenter, T. Wade, R.L. Calderon, 

J.M. Roberts, M.J. Beach, and S.L. Roy. 2010. Causes of outbreaks associated with drinking 

water in the United States from 1971 to 2006. Clinical Microbiology Reviews, 23(3): 507-528. 

Crespi, S., and J. Ferra. 1998. Chlorination and thermal treatment in the control of Legionella in 

hotels: 5 years follow-up. 13th Meeting of the European Working Group on Legionella

Infections, Abstract 3. 

Cristino, S., P.P. Legnani, and E. Leoni. 2012. Plan for the control of Legionella infections in 

long-term care facilities: Role of environmental monitoring. International Journal of Hygiene 

and Environmental Health, 215(2012): 279-285. 

Cunha, B.A. 2006. The atypical pneumonias: clinical diagnosis and importance. Clinical 

Microbiology and Infection, 12(Suppl. 3): 12-24. 

Cunliffe, D.A. 1990. Inactivation of Legionella pneumophila by monochloramine. Applied 

Bacteriology, 68: 453-459. 

Daeschlein, G., W.H. Krüger, C. Selepko, M. Rochow, G. Dölken, and A. Kramer. 2007. 

Hygienic safety of reusable tap water filters (GermLyser®) with an operating time of 4 or 8 

weeks in a haematological oncology transplant unit. BMC Infectious Diseases, 7:45. 

Darelid, J., S. Löfgrenm, and B.E. Malmvall. 2002. Control of nosocomial Legionnaires' disease 

by keeping the circulating hot water temperature above 55 degrees C: experience from a 10-year 

surveillance programme in a district general hospital. Hospital Infection, 50(3): 213-219. 

de Beer, D., R. Srinivasan, and P.S. Stewart. 1994. Direct measurement of chlorine penetration 

into biofilms during disinfection. Applied and Environmental Microbiology. 60(12): 4339–4344. 

Deere, D., and A. Davison. 1998. Safe drinking water. Are food guidelines the answer? Water,

Nov/Dec.

Department of Homeland Security. 2015. Chemical Facility Anti-Terrorism Standards (CFATS). 

Available online at http://www.dhs.gov/chemical-facility-anti-terrorism-standards. 

Department of Veterans Affairs. 2012. Indoor water features, decorative fountains: recommend 

non-use. 003C2B-DA-138. 

Department of Veterans Affairs. 2014. VHA Directive 1061. Prevention of healthcare-associated 

Legionella disease and scald injury from potable water distribution systems. Washington, DC: 

Veterans Health Administration.

Dietrich, A.M. 2009. The sense of smell: contributions of orthonasal and retronasal perception 

applied to metallic flavor of drinking water. Journal of Water Supply: Research and Technology 

– AQUA, 58(8): 562-570. 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 74 October 2015 

Dietrich, A.M. and R. Hoehn, 1991. Taste and odor problems associated with chlorine dioxide. 

Denver, Colo.: Water Research Foundation and AWWA. 

Doleans A., H. Aurell, M. Reyrolle, G. Lena, J. Freney, F. Vandenesch, J. Etienne, and S. 

Jarraud. 2004. Clinical and environmental distributions of Legionella strains in France are 

different. J Clin Microbiol, 42(1):458-60. 

Domingue, E.L., R.L. Tyndall, W.R. Mayberry, and O.C. Pancorbo. 1988. Effects of Three 

Oxidizing Biocides on Legionella pneumophila Serogroup 1. Applied and Environmental 

Microbiology, 54(3): 741-747. 

Dondero, T.J., H.W. Clegg, T.F. Tsai, R.M. Weeks, E. Duncan, J. Strickler, C. Chapman, G.F. 

Mallison, B. Politi, M.E. Potter, and W. Schaffner. 1979. Legionnaires’ disease in Kingsport, 

Tennessee. Annals of Internal Medicine, 90: 569-573. 

Donlan, R., R. Murga, J. Carpenter, E. Brown, R. Besser, and B. Fields. 2002. Monochloramine 

disinfection of biofilm-associated Legionella pneumophila in a potable water model system. In: 

Legionella, R. Marre, Y.A. Kwaik, and C. Bartlett, (eds.). 406-410. Washington, DC: American 

Society for Microbiology. 

Donohue, M.J., K.O. O’Connell, S.J. Vesper, J.H. Mistry, D. King, M. Kostich, and S. Pfaller. 

2014. Widespread molecular detection of Legionella pneumophila serogroup 1 in cold water taps 

across the United States. Environmental Science & Technology, 48: 3145-3152. 

Drake, P.L. and K.J. Hazelwood. 2005. Exposure-Related Health Effects of Silver and Silver 

Compounds: A Review. Annals of Occupational Hygiene, 49:575-585. 

DSMZ. 2014. List of prokaryotic names validly published. Braunschweig, Germany. Available 

online at: 

http://www.dsmz.de/fileadmin/Bereiche/ChiefEditors/BacterialNomenclature/DSMZ_Bactnames

.pdf. 

Ducret, A., M. Chabalier, and S. Dukan. 2014. Characterization and resuscitation of ‘nonculturable’ cells of Legionella pneumophila. BMC Microbiology, 14: 3-10. 

Duda, S.,S. Kandiah, J.E. Stout, J.L. Baron, M. Yassin, M. Fabrizio, J. Ferrelli, R. Hariri, M.M. 

Wagener, J. Goepfert, J. Bond, J. Hannigan, and D. Rogers. 2014. Evaluation of a New 

Monochloramine Generation System for Controlling Legionella in Building Hot Water Systems. 

Infection Control and Hospital Epidemiology, 35(11): 1356-1363. 

Dupuy, M., S. Mazoua, F. Berne, C. Bodet, N. Garrec, P. Herbelin, F. Menard-Szczebara, S. 

Oberti, M.H. Rodier, S. Soreau, F. Wallet, and Y. Héchard. 2011. Efficiency of water 

disinfectants against Legionella pneumophila and Acanthamoeba. Water Research, 45: 1087-

1094. 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 75 October 2015 

Dyck, A., M. Exner, and A. Kramer. 2007. Experimental based experiences with the introduction 

of a water safety plan for a multi-located university clinic and its efficacy according to WHO 

recommendations. BMC Public Health, 7(34). 

Edelstein, P.H. 2007. Legionella*. In Manual of Clinical Microbiology, 9th ed., P.R. Murray 

(ed.). p. 835-849. Washington, DC: ASM Press. 

Edelstein, P.H., R.E. Whittaker, R.L. Kreiling, and C.L. Howell. 1982. Efficacy of Ozone in 

Eradication of Legionella pneumophila from Hospital Plumbing Fixtures. Applied and 

Environmental Microbiology, 44(6): 1330-1334. 

Edwards, M. and A. Dudi. 2004. Role of chlorine and chloramines in corrosion of lead-bearing 

plumbing materials. Journal AWWA, 96(10): 69-81. 

Edwards, M., J.F. Ferguson, and S.H. Reiber. 1994. The pitting corrosion of copper. Journal 

AWWA, 86: 74-90. 

Edwards, M., S. Jacobs, and R.J. Taylor. 2000. The blue water phenomenon. Journal AWWA,

92(7):72-82.

Escoll, P., M. Rolando, L. Gomez-Valero and C. Buchrieser. 2013. From amoeba to 

macrophages: exploring the molecular mechanisms of Legionella pneumophila infection in both 

hosts. Current Topics in Microbiology and Immunology, 376: 1-34. 

Euser S.M., J.P. Bruin, P. Brandsema, L. Reijnen, S.A. Boers, and J.W. Den Boer. 2013. 

Legionella prevention in the Netherlands: an evaluation using genotype distribution. Eur J Clin 

Microbiol Infect Dis, 32(8): 1017-22. 

Fang, G.D., V.L. Yu, and R.M. Vickers. 1989. Disease due to the Legionellaceae (other than 

Legionella pneumophila). Historical, microbiological, clinical and epidemiological review. 

Medicine Baltimore, 68(2): 116-132. 

Fields, B. S. 1996. The molecular ecology of Legionellae. Trends in Microbiology, 4(7): 286-

290. 

Fields, B.S., R.F. Benson, and R.E. Besser, 2002. Legionella and Legionnaires' disease: 25 years 

of investigation. Clinical Microbiology Reviews, 15: 506-26. 

Fields B.S., E.B. Shotts, J.C. Feeley, G.W. Gorman, and W.T. Martin. 1984. Proliferation of 

Legionella pneumophila as an intracellular parasite of the ciliated protozoan Tetrahymena 

pyriformis. Applied and Environmental Microbiology, 47: 467-471. 

Figueras, M.J., and J.J. Borrego. 2010. New perspectives in monitoring drinking water microbial 

quality. International Journal of Environmental Research and Public Health, 7: 4179-4202. 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 76 October 2015 

Fitzgeorge, R.B., A. Baskerville, M. Broster, P. Hambleton, and P.J. Dennis. 1983. Aerosol 

infection of animals with strains of Legionella pneumophila of different virulence: comparison 

with intraperitoneal and intranasal routes of infection. Journal of Hygiene, 90: 81 – 89. 

Flannery, B., L.B. Gelling, D.J. Vugia, J.M. Weintraub, J.J. Salerno, M.J. Conroy, V.A. Stevens, 

C.E. Rose, M.R. Moore, B.S. Fields, and R.E. Besser. 2006. Reducing Legionella colonization of 

water systems with monochloramine. Emerging Infectious Diseases, 12(4): 588-596. 

Fliermans, C.B., W.B. Cherry, L.H. Orrison, S.J. Smith, D.L. Tison, and D.H. Pope. 1981. 

Ecological distribution of Legionella pneumophila. Applied and Environmental Microbiology,

41: 9-16. 

Food and Agriculture Organization (FAO). 1998. Food quality and safety systems - a training 

manual on food hygiene and the hazard analysis and critical control point (HACCP) system. 

Food and Agriculture Organization of the United Nations Publishing Management Group, FAO 

Information Division, Rome. Available online at: 

http://www.fao.org/docrep/W8088E/w8088e05.htm#section. 

Franzin, L., D. Cabodi, and C. Fantino. 2002. Evaluation of the efficacy of ultraviolet irradiation 

for disinfection of hospital water contaminated by Legionella. Hospital Infection, 51(4): 269. 

Franzin, L, C. Scolfaro, D. Cabodi, M. Valera, and P. A. Tovo. 2001. Legionella pneumophila

pneumonia in a newborn after water birth: a new mode of transmission. Clinical Infectious 

Diseases – Brief Report, 33: e103. 

Fraser, D.W., T.R. Tsai, W. Orenstein, W.E. Parkin, H.J. Beecham, R.G. Sharrar, J. Harris, G.F. 

Mallison, S.M. Martin, J.E. McDade, C.C. Shepard, and P.S. Brachman. 1977. Legionnaires’ 

disease: description of an epidemic of pneumonia. New England Journal of Medicine. 297: 

n1186-1196. 

García, M.T., B. Baladrón, V. Gil, M.L. Tarancon, A. Vilasau, A. Ibañez, C. Elola, and C. Pelaz. 

2008. Persistence of chlorine-sensitive Legionella pneumophila in hyperchlorinated installations. 

Applied Microbiology, 105(3): 837-847. 

Gates, D., G. Ziglio, and K. Ozekin. 2009. State of the Science of Chlorine Dioxide in Drinking 

Water. Water Research Foundation and Fondazione AMGA. 

Gillilland, C., A.A. Rosenblatt, and W.F. McCoy. 2014. HACCP for building water systems. 

Water Conditioning and Purification International. Jan.

Gilpin, R. W., S.B. Dillon, P. Keyser, A. Androkites, M. Berube, N. Carpendale, J. Skorina, J. 

Hurley, and A.M. Kaplan. 1985. Disinfection of circulating water systems by ultraviolet light 

and halogenation. Water Research, 19(7): 839-848. 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 77 October 2015 

Glick, T.H., M.B. Gregg, B. Berman, G. Mallison, W.W. Rhodes Jr., and I. Kassanoff. 1978. 

Pontiac fever. An epidemic of unknown etiology in a health department: I. Clinical and 

epidemiological aspects. American Journal of Epidemiology, 107(2): 149-160. 

Graman, P.S., G.A. Quinlan, and J.A. Rank. 1997. Nosocomial legionellosis traced to a 

contaminated ice machine. Infection Control and Hospital Epidemiology. 18(9): 637-640.

Gray, R., and M. Morain. 2000. HACCP application to Brisbane water. Water, Jan/Feb. 

Great Lakes – Upper Mississippi River Board of State and Provincial Public Health and 

Environmental Managers (GLUMRBSPPHEM). 2012. Recommended Standards for Water Works. 

Health Education Service, Albany, NY.

Grosserode, M., R. Wenzel, M. Pfaller, and C. Helms. 1993. Continuous hyperchlorination for 

control of nosocomial Legionella pneumophila pneumonia: a 10-year follow-up of efficacy, 

environmental effects, and costs. In: Legionella: current status and emerging perspectives, J.M. 

Barbaree, R.F. Breiman, A.P. Dufour, (eds.). 226-229. Washington, DC: American Society of 

Microbiology. 

Gunnarsdóttir, M.J., and L.R. Gissurarson. 2008. HACCP and water safety plans in Icelandic 

water supply: Preliminary evaluation of experience. Water and Health, 6(3): 377-382. 

Hall, K.K., E.T. Gianetta, S. I. Getchell-White, L. J. Durbin, and B. M. Farr. 2003. Ultraviolet 

light disinfection of hospital water for preventing nosocomial Legionella infection: a 13-year 

follow-up. Infection Control and Hospital Epidemiology, 24(8): 580-583. 

Harrison T.G., B. Afshar, N. Doshi, N.K. Fry, and J.V. Lee. 2009. Distribution of Legionella 

pneumophila serogroups, monoclonal antibody subgroups and DNA sequence types in recent 

clinical and environmental isolates from England and Wales (2000-2008). Eur J Clin Microbiol 

Infect Dis, 28(7): 781-91. 

Haupt, T.E., R.T. Heffernan, J.J. Kazmierczak, H. Nehls-Lowe, B. Rheineck, C. Powell, K.K. 

Leonhardt, A.S. Chitnis, and J.P Davis. 2012. An outbreak of Legionnaires disease associated 

with a decorative water wall fountain in a hospital. Infection Control and Hospital Epidemiology,

33(2): 185-191. 

Havelaar, A.H. 1994. Application of HACCP to drinking water supply. Food Control, 5(3): 145-

152. 

Health and Safety Executive (HSE). 2009. National Guidelines for the Control of Legionellosis 

in Ireland.

Health and Safety Executive (HSE). 2014. Legionnaires’ disease part 2: The control of Legionella

bacteria in hot and cold water systems. HSG274 Part 2. 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 78 October 2015 

Health Canada. 2013. Guidance on waterborne bacterial pathogens. Water, Air and Climate 

Change Bureau, Health Environments and Consumer Safety Branch, Health Canada, Ottawa, 

Ontario (Catalogue No. H129-25/1-2014E-PDF).

Health Protection Surveillance Centre. 2009. National Guidelines for the Control of 

Legionellosis in Ireland, 2009. Report of Legionnaires’ Disease Subcommittee of the Scientific 

Advisory Committee. Dublin, Ireland: Health Protection Surveillance Centre.

Heffelfinger, J.D., J.L. Kool, S. Fridkin, V.J. Fraser, J. Hageman, J. Carpenter, and C.G. 

Whitney. 2003. Risk of hospital-acquired Legionnaires’ disease in cities using monochloramine 

versus other water disinfectants. Infection Control and Hospital Epidemiology, 24(8): 569-574. 

Heimberger, T., G. Birkhead, D. Bornstein, K. Same, and D. Morse. 1991. Control of 

nosocomial Legionnaires’ disease through hot water flushing and supplemental chlorination of 

potable water. Infectious Diseases, 163(2): 413. 

Heng, B.H., K.T. Goh, and L.K. Ng. 1995. Surveillance and control of Legionella bacteria in the 

built environment. In Health and the Built Environment. Singapore: Ministry of the 

Environment. 

Hoffman, C., C.F. Harrison, and H. Hilbi. 2014. The natural alternative: protozoa as cellular 

models for Legionella infection. Cellular Microbiology, 16(1): 15-26. 

Hong, J-H; S.E. Duncan, A.M. Dietrich. 2010. Effect of copper speciation at different pH on 

temporal sensory attributes of copper. Food Quality and Preference, 21(1): 132-139. 

Huang, H.I., H.Y. Shih, C.M. Lee, T.C. Yang, J.J. Lay, and Y.E. Lin. 2008. In vitro efficacy of 

copper and silver ions in eradication Pseudomonas aeruginosa, Stenotrophomonas maltophilia

and Acinetobacter baumannii: implications for on-site disinfection for hospital infection control. 

Water Research, 42(1-2): 73-80. 

Hung, L., D.C. Copperthite, C.S. Yang, F.A. Lewis, and F.A. Zampiello. 1993. Environmental 

Legionella assessment in office buildings of continental United States. Indoor Air, 3: 349-353. 

Hwang, M.G., H. Katayama, and S. Ohgaki. 2007. Inactivation of Legionella pneumophila and 

Pseudomonas aeruginosa: evaluation of the bactericidal ability of silver cations. Water 

Research, 41:4097-4104. 

Jacangelo, J.G., N.L. Patania, R.R. Trussel, C.N. Haas, and C. Gerba. 2002. Inactivation of 

Waterborne Emerging Pathogens by Selected Disinfectants. Denver, Colo.: AWWA Research 

Foundation and AWWA. 

Jakubek, D., C. Guillaume, M. Binet, G. Leblon, M. Dubow, and M. Le Brun. 2013. 

Susceptibility of Legionella strains to the chlorinated biocide, monochloramine. Microbes and 

Environments, 28(3): 336-345. 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 79 October 2015 

Kana, B.D., B.G. Gordhan, K. J. Downing, N. Sung, G.Vostroktunova, E. E. Machowski, 

L.Tsenova, M.Young, A. Kaprelyants, G. Kaplan, and V. Mizrahi. 2008. The resuscitationpromoting factors of Mycobacterium tuberculosis are required for virulence and resuscitation 

from dormancy but are collectively dispensable for growth in vitro. Molecular Microbiology,

67(3): 672-684. 

Katz, S.M., and J.M. Hammel. 1987. The effect of drying, heat and pH on the survival of 

Legionella pneumophila. Annals of Clinical and Laboratory Science, 17(3): 150-156. 

Kaufmann A.F., J.E. McDade, C.M. Patton, J.V. Bennett, P. Skaliy, J.C. Feeley, D.C. Anderson, 

M.E. Potter, V.F. Newhouse, M.B. Gregg, and P.S. Brachman. 1981. Pontiac fever: isolation of 

the etiologic agent (Legionella pneumophila) and demonstration of its mode of transmission. 

American Journal of Epidemiology114(3): 337-47. 

Kilvington, S. and J. Price, 1990. Survival of Legionella pneumophila within cysts of 

Acanthamoeba polyphaga following chlorine exposure. Applied Bacteriology, 68: 519-525. 

Kim, B.R., J.E. Anderson, S.A. Mueller, W.A. Gaines, and A.M. Kendall, 2002. Literature 

review – efficacy of various disinfectants against Legionella in water systems. Water Research,

36(18): 4433-4444. 

Kirk-Othmer. 1979. Kirk-Othmer Encyclopedia of Chemical Technology, 3rd ed. 

Kirmeyer, G., K. Martel, G. Thompson, L. Radder, W. Klement, M. LeChevallier, H. Baribeau, 

and A. Flores. 2004. Optimizing Chloramine Treatment. Denver, Colo. Water Research 

Foundation and AWWA.

Knobeloch L., C. Schubert, J. Hayes, J. Clark, C. Fitzgerald, and A. Fraundorff. 1998. 

Gastrointestinal Upsets and New Copper Plumbing - Is There a Connection? Wisconsin Medical 

Journal, 49-53. 

Knobeloch, L., M. Ziarnik, J. Howard, B. Theis, D. Farmer, H. Anderson, and M. Proctor. 1994. 

Gastrointestinal upsets associated with ingestion of copper-contaminated water. Environmental 

Health Perspectives, 102(11): 958-961. 

Knudson, G.B. 1985. Photoreactivation of UV-irradiated Legionella pneumophila and other 

Legionella species. Applied and Environmental Microbiology, 49(4): 975-980. 

Kool, J.L., J.C. Carpenter, and B.S. Fields. 1999. Effect of monochloramine disinfection of 

municipal drinking water on risk of nosocomial Legionnaires’ disease. The Lancet, 353: 272-

277. 

Kool, J.L., J.C. Carpenter, and B.S. Fields. 2000. Monochloramine and Legionnaires’ disease. 

Journal AWWA, 92(9): 88-96 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 80 October 2015 

Kozak N.A., R.F. Benson, E. Brown, N.T. Alexander, T.H. Taylor Jr., B.G. Shelton, and B.S. 

Fields. 2009. Distribution of lag-1 alleles and sequence-based types among Legionella 

pneumophila serogroup 1 clinical and environmental isolates in the United States. J Clin 

Microbiol, 47(8): 2525-35. 

 Kozak, N.A., C.E. Lucas, and J.M. Winchell. 2013. Identification of Legionella in the 

environment. In: Legionella: Methods and Protocols, Methods in Molecular Biology Vol. 954,

Carmen Buchrieser and Hubert Hilbi (eds). p 3-25. New York: Springer + Business Media.

Kozak-Muiznieks N.A., Lucas C.E., Brown E., T. Pondo, T.H. Taylor Jr., M. Frace, D. 

Miskowski, and J. M. Winchell. 2014. Prevalence of sequence types among clinical and 

environmental isolates of Legionella pneumophila serogroup 1 in the United States from 1982 to 

2012. J Clin Microbiol, 52(1): 201-211. 

Krageschmidt, D.A., A.F. Kubly, M.S. Browning, A.J. Wright, J.D. Lonneman, M.J. Detmer, 

and W.F. McCoy. 2014. A comprehensive water management program for multicampus 

healthcare facilities. Infection Control and Hospital Epidemiology, 35(5): 556-563. 

Kuchta, J.M., S.J. States, A.M. McNamara, R.M. Wadowsky, and R.B. Yee. 1983. Susceptibility 

of Legionella pneumophila to Chlorine in Tap Water. Applied and Environmental Microbiology,

46(5): 1134-1139. 

Kusnetsov, J., E. Iivanainen, N. Elomaa, O. Zacheus, and P.J. Martikainen. 2001. Copper and 

silver ions more effective against Legionellae than against mycobacteria in a hospital warm 

water system. Water Research, 35(17): 4217-25. 

Kwaik, Y.A., L.Y. Gao, B.J. Stone, C. Venkataraman, and O.S. Harb. 1998. Invasion of protozoa 

by Legionella pneumophila and its role in bacterial ecology and pathogenesis. Applied and 

Environmental Microbiology. 64(9): 3127-3133.

Landeen, L.K., M.T. Yahya, and C.P. Gerba. 1989. Efficacy of copper and silver ions and 

reduced levels of free chlorine in inactivation of Legionella pneumophila. Applied and 

Environmental Microbiology, 55(12): 3045-50. 

LeChevallier, M.W., C.D. Cawthon, and R.G. Lee. 1988a. Inactivation of biofilm bacteria. 

Applied and Environmental Microbiology, 54(10): 2492-2499. 

LeChevallier, M.W., C.D. Cawthon, and R.G. Lee. 1988b. Factors promoting survival of bacteria

in chlorinated water supplies. Applied and Environmental Microbiology, 54(3): 649-654. 

Lee, W.H., D.G. Wahman, P.L. Bishop, and J.G. Pressman. 2011. Free chlorine and 

monochloramine application to nitrifying biofilm: Comparison of biofilm penetration, activity 

and viability. Environmental Science and Technology, 45, 1412-1419. 

Lee, W., P. Westerhoff, X. Yang, and C. Shang. 2007. Comparison of colorimetric and 

membrane introduction mass spectrometry techniques for chloramine analysis. Water Res., 

41(14): 3097-3102. 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 81 October 2015 

Lin, Y.E., J.E. Stout, and V.L. Yu. 2011a. Prevention of hospital–acquired legionellosis. Current 

Opinion in Infectious Diseases, 24: 350-356. 

Lin, Y.E., J.E. Stout, and V.L. Yu. 2011b. Controlling Legionella in hospital drinking water: An 

evidence-based review of disinfection methods. Infection Control and Hospital Epidemiology,

32(2): 166-173. 

Lin, Y.E., J.E. Stout, V.L. Yu, R.D. Vidic, and S.J. States. 2000b. Legionnaires disease in an 

apartment building: disinfection methods and recommendations. Abstract for Health-related 

Water Microbiology Symposium. Submitted for oral presentation at 1st International Water 

Congress, International Water Association. Paris, France. July 3-7, 2000. 

Lin, Y.E., R.D. Vidic, J.E. Stout, C.A. McCartney, and V.L. Yu. 1998b. Inactivation of 

Mycobacterium avium by copper and silver ions. Water Research. 32(7): 1997-2000. 

Lin, Y.E., R.D. Vidic, J.E. Stout, and V.L. Yu. 1996. Individual and combined effects of copper 

and silver ions on inactivation of Legionella pneumophila. Water Research, 30(8): 1905-13. 

Lin, Y.E., R.D. Vidic, J.E. Stout, and V.L. Yu. 1998a. Legionella in water distribution systems. 

Journal AWWA, 90(9), 112-122. 

Lin, Y.E., R.D. Vidic, J. E. Stout, and V.L. Yu. 2002. Negative effect of high pH on biocidal 

efficacy of copper and silver ions in controlling Legionella pneumophila. Applied and 

Environmental Microbiology, 68(6): 2711-15. 

Lin, Y.E., V.L. Yu, R.D. Vidic, and S.J. States. 2000a. Discussion of “monochloramine and 

Legionnaires’ disease.” American Water Works Association. 92(10): 88-90. 

Liu, Z., J.E. Stout, M. Boldin, J. Rugh, W. Diven, and V.L. Yu. 1998. Intermittent use of coppersilver ionization for Legionella control in water distribution systems: a potential option in 

buildings housing individuals at low risk of infection. Clinical Infectious Diseases, 26: 138-140. 

Liu, Z., J.E. Stout, L. Tedesco, M. Boldin, C. Hwang, W.F. Diven, and V.L. Yu. 1994. 

Controlled evaluation of copper-silver ionization in eradicating Legionella pneumophila from a 

hospital water distribution system. Infectious Diseases, 169: 919-922. 

Liu, Z., J.E. Stout, L. Tedesco, M. Boldin, C. Hwang, and V.L. Yu. 1995. Efficacy of UV light in 

preventing Legionella colonization of a hospital water distribution system. Water Research,

29(10): 2275-2280. 

Loret, J.F., S. Robert, V. Thomas, A.J. Cooper, W.F. McCoy, and Y. Lévi. 2005. Comparison of 

disinfectants for biofilm, protozoa and Legionella control. IWA Journal of Water and Health, 

3(4): 423-433. 

LPSN. 2014. (List of prokaryotic names with standing in nomenclature ().) Available online at: 

http://www.bacterio.net/Legionella.htmL. 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 82 October 2015 

Lucas, C.E., T.H. Taylor Jr., and B.S. Fields. 2011. Accuracy and precision of Legionella

isolation by US laboratories in the ELITE program pilot study. Water Research, 45: 4428-4436. 

Lytle, D.A., and M.R. Schock. 2007. Pitting Corrosion of Copper in Waters with High pH and 

Low Alkalinity. JAWWA, 100(3):115-129. 

Marchesi, I., S. Cencetti, P. Marchegiano, G. Frezza, P. Borella, and A. Bargellini. 2012. Control 

of Legionella contamination in a hospital water distribution system by monochloramine.

American Journal of Infection Control, 40: 279-281. 

Marchesi, I., G. Ferranti, A. Bargellini, P. Marchegiano, G. Predieri, J.E. Stout, and P. Borella. 

2013. Monochloramine and chlorine dioxide for controlling Legionella pneumophila

contamination: biocide levels and disinfection byproduct formation in hospital networks. IWA

Journal of Water and Health, 11(4): 738-747. 

Marchesi, I., P. Marchegiano, A. Bargellini, S. Cencetti, G. Frezza, M. Miselli, and P. Borella. 

2011. Effectiveness of different methods to control Legionella in the water supply: ten-year 

experience in an Italian university hospital. Hospital Infection. 77(1): 47-51. 

Marston, B.J., H.B. Lipman, and R.F. Breiman. 1994. Surveillance for Legionnaires’ disease. 

Risk factors for morbidity and mortality. Archives of Internal Medicine, 154(21): 2417-2422. 

Marston, B.J., J.F. Plouffe, T.M. File Jr., B.A. Hackman, S.J. Salstrom, H.B. Lipman, M.S. 

Kolczak, and R.F. Breiman. 1997. Incidence of community-acquired pneumonia requiring 

hospitalization: Results of a population-based active surveillance study in Ohio. Archives of 

Internal Medicine, 157(15): 1709-1718. 

Martel, K., G. Kirmeyer, A. Hanson, M. Stevens, J. Mullenger, and D. Deere. 2006. Application 

of HACCP for distribution system protection. Denver, Colo.: Water Research Foundation. 

McDade, J.E., D.J. Brenner, and F.M. Bozeman. 1979. Legionnaires’ disease bacterium isolated 

in 1947. Annals of Internal Medicine, 90: 659-661. 

Miami-Dade County Health Department (MDCHD). 2010. Outbreak of Legionnaire’s disease: 

Miami-Dade County Health Department Final Report. Miami, FL. 

Mietzner, S., R.C. Schwille, A. Farley, E.R. Wald, J.H. Ge, S.J. States, T. Libert, R.M. 

Wadowsky. 1997. Efficacy of thermal treatment and copper-silver ionization for controlling 

Legionella pneumophila in high-volume hot water plumbing systems in hospitals. American 

Journal of Infection Control, 25(6): 452-457. 

Mòdol, J., M. Sabria, E. Reynaga, M.L. Pedro-Botet, N. Sopena, P. Tudela, I. Casas, and C. ReyJoly. 2007. Hospital-acquired Legionnaires disease in a university hospital: impact of the coppersilver ionization system. Clinical Infectious Diseases, 44: 263-265. 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 83 October 2015 

Molloy, S.L., R. Ives, A. Hoyt, R. Taylor, and J.B. Rose. 2008. The use of copper and silver in 

carbon point-of-use filters for the suppression of Legionella throughput in domestic water 

systems. Applied Microbiology, 104: 998-1007. 

Molmeret, M., D.M. Bitar, L. Han, and Y.A. Kwaik. 2004. Cell biology of the intracellular 

infection by Legionella pneumophila. Microbes and Infection. 6(1): 129-139. 

Moore, M.R., M. Pryor, B. Fields, C. Lucas, M. Phelan, and R.E. Besser. 2006. Introduction of 

monochloramine into a municipal water system: Impact on colonization of buildings by 

Legionella spp. Applied and Environmental Microbiology, 72: 378-383. 

Mortimore, S.E. and C.A. Wallace. 2001. HACCP, Blackwell Science, UK.

Muder, R.R., V.L. Yu, and A.H. Woo. 1986. Mode of transmission of Legionella pneumophila: a 

critical review. Archives of Internal Medicine, 146: 1607-1612.

Mullenger, J., G. Ryan, and J. Hearn. 2002. A water authority’s experience with HACCP. Water 

Science and Technology, 2(5-6): 149-155. 

Muraca, P., J.E. Stout, and V.L.Yu. 1987. Comparative assessment of chorine, heat, ozone and 

UV light for killing Legionella pneumophila within a model plumbing system. Applied and 

Environmental Microbiology, 53(2): 447-453. 

Nagai, T., H. Sobajima, M. Iwasa, T. Tsuzuki, F. Kura, J. Amemura-Maekawa, and H. 

Watanabe. 2003. Neonatal sudden death due to Legionella pneumonia associated with water 

birth in a domestic spa bath. Clinical Microbiology, 41(5): 2227-2229. 

National Environmental Methods Index. Available online at: http://www.nemi.gov/home/. 

Accessed October 1, 2014. 

Newton, H.J., D.K. Ang, I.R. van Driel, and E.L. Hartland. 2010. Molecular pathogenesis of 

infections caused by Legionella pneumophila. Clinical Microbiology Reviews, 23(2): 274-298. 

Niedeveld, C.J., F.M. Pet, and P.L. Meenhorst. 1986. Effect of rubbers and their constituents on 

proliferation of Legionella pneumophila in naturally contaminated hot water. Lancet, II: 180-

184. 

Nies, D. H. 1999. Microbial heavy-metal resistance. Applied Microbiology Biotechnology,

51:730-50. 

O’Brien, S.J. and R.S. Bhopal. 1993. Legionnaires’ disease: the infective dose paradox. Lancet,

342:5.

Occupational Safety and Health Administration (OSHA). 1999. OSHA Technical Manual. TED 

01-00-015. Section III, Chapter 7. Available online at: 

http://www.osha.gov/dts/osta/otm/otm_iii/otm_iii_7.htmL. 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 84 October 2015 

Oguma, K., H. Katayama and S. Ohgaki. 2004. Photoreactivation of Legionella pneumophila

after inactivation by low- or medium-pressure ultraviolet lamp. Water Research, 38(11): 2757-

2763 

Ohno, A., N. Kato, R. Sakamoto, S. Kimura, and K. Yamaguchi. 2008. Temperature-dependent 

parasitic relationship between Legionella pneumophila and a free-living amoeba (Acanthamoeba 

castellanii). Applied and Environmental Microbiology, 74(14): 4585-4588. 

Oliver, J.D. 2010. Recent findings on the viable but nonculturable state in pathogenic bacteria. 

FEMS Microbiology Reviews, 34: 415-425. 

Orsi, G.B., M. Vitali, L. Marinelli, V. Ciorba, D. Tufi, A. Del Cimmuto, P. Ursillo, M. Fabiani, 

S. DeSantis, C. Protano, C. Marzuillo, and M. DeGiusti. 2014. Legionella control in the water 

system of antiquated hospital buildings by shock and continuous hyperchlorination: 5 years’ 

experience. BMC Infectious Diseases, 14: 394. Available online at: 

http://www.biomedcentral.com/content/pdf/1471-2334-14-394.pdf. 

Ortolano, G.A., M.B. McAlister, J.A. Angelbeck, J. Schaffer, R.L. Russell, E. Maynard, and B. 

Wenz. 2005. Hospital water point-of-use filtration: A complementary strategy to reduce the risk 

of nosocomial infection. American Journal of Infection Control, 33(5): S1-S19. 

Pearce, M.M., N. Theodoropoulos, M.J. Mandel, E. Brown, K.D. Reed, and N.P. Cianciotto. 

2012. Legionella cardiaca sp. nov., isolated from a case of native valve endocarditis in a human 

heart. International Journal of Systematic and Evolutionary Microbiology, 62: 2946-2954. 

Pedro-Botet, M.L., I. Sanchez, M. Sabria, N. Sopena, L. Mateu, M. Garcia-Nunez, and C. ReyJoly. 2007. Impact of copper and silver ionization on fungal colonization of the water supply in 

health care centers: implications for immunocompromised patients. Clinical Infectious Diseases.

45: 84-86. 

Pressman, J.G., W.H. Lee, P.L. Bishop, and D.G. Wahman. 2012. Effect of free ammonia 

concentration on monochloramine penetration within a nitrifying biofilm and its effect on 

activity, viability and recovery, Water Research, 46(3), 882-894. 

Pruden, A., M.A. Edwards, and J.O. Falkinham, III. 2013. State of the science and research 

needs for opportunistic pathogens in premise plumbing. Water Research Foundation.

Pryor, M., S. Springthorpe, S. Riffard, T. Brooks, Y. Huo, G. Davis, and S.A. Sattar. 2004. 

Investigation of opportunistic pathogens in municipal drinking water under different supply and 

treatment regimes. Water Science and Technology, 50(1): 83-90. 

Public Health England. 2014. Public Health England advice on home birthing pools. Available 

online at: http://www.gov.uk/government/news/public-health-england-advice-on-home-birthingpools. 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 85 October 2015 

Reingold, A.L., B.M. Thomason, B.J. Brake, L. Thacker, H.W. Wilkinson, and J.N. Kuritsky. 

1984. Legionella pneumonia in the United States: the distribution of serogroups and species 

causing human illness. Infectious Diseases, 149(5): 819. 

Rhoads, W.J., A. Pruden, and M.A. Edwards. 2014. Anticipating challenges with in-building 

disinfection for control of opportunistic pathogens. Water Environment Research. 86(6): 540-

549. 

Richards, A.M., J.E. Von Dwingelo, C.T. Price and Y.A. Kwaik. 2013. Cellular microbiology 

and molecular ecology of Legionella-amoeba interaction. Virulence, 4(4): 307-314. 

Roche, P. and D. Benanou, 2007. Impact of chlorination on the formation of odor compounds 

and their precursors in treatment of drinking water. Available online at: 

http://www.techneau.org/fileadmin/files/Publications/Publications/Deliverables/D5.3.8.pdf. 

Rohr, U., M. Senger, F. Selenka, R. Turley, and M. Wilhelm. 1999. Four years of experience 

with silver-copper ionization for control of Legionella in a German university hospital hot water 

plumbing system. Clinical Infectious Diseases, 29: 1507-11. 

Rohr, U., S. Weber, F. Selenka, and M. Wilhelm. 2000. Impact of silver and copper on the 

survival of amoebae and ciliated protozoa in vitro. International Journal of Hygiene and 

Environmental Health, 203: 87-89. 

Rosenblatt, A.A. and W.F. McCoy. 2014. HACCP for Building Water Systems. Participants’ 

Handbook. Version 1.0. NSF International. 

Rowbotham, T.J. 1986. Current views on the relationships between amoebae, Legionellae and 

man. Israel Journal of Medical Sciences. 22(9): 678-689. 

Ruiz, B., J. Bauzá, J. Benito, and A. Pascual. 2007. Use of ozone for Legionella reduction in 

water systems. IOA Conference and Exhibition, Spain. October 29-31, 2007. 

Rusin, P.A., J.B. Rose, C.N. Haas, and C.P. Gerba. 1997. Risk assessment of opportunistic 

bacterial pathogens in drinking water. Reviews of Environmental Contamination and Toxicology. 

152: 57-83. 

Saby, S., A. Vidal and H. Suty. 2005. Resistance of Legionella to disinfection in hot water 

systems. Water Science and Technology. 52(8): 15-26. 

Sarver, E., K. Dodson, R.P. Scardina, R. Lattyak-Slabaugh, M. Edwards, and C. Nguyen. 2011. 

Copper pitting in chlorinated, high-pH potable water. Journal AWWA, 103(3): 86-97. 

Schaechter, M., N.C. Engelberg, B.I. Eisenstein, and G. Medoff. 1998. Mechanisms of microbial 

disease. Third Edition. Williams and Wilkins. Baltimore, MD.

Schoen, M.E., and N.J. Ashbolt. 2011. An in-premise model for Legionella exposure during 

showering events. Water Research. 45: 5826 – 5836. 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 86 October 2015 

Sehulster, L., and R.Y.W. Chinn. 2003. Guidelines for Environmental Infection Control in 

Health-Care Facilities, 2003: Recommendations of CDC and the Healthcare Infection Control 

Practices Advisory Committee. Morbidity and Mortality Weekly Report. 52:1-44. Available 

online at: http://www.cdc.gov/hicpac/pdf/guidelines/eic_in_HCF_03.pdf 

Seidel, C.J., M.J. McGuire, R.S. Summers, and S. Via. 2005. Have utilities switched to 

chloramines? Journal AWWA. 97(10): 87-97. 

Shah, A. and W.A. Mitch. 2012. Halonitroalkanes, Halonitriles, Haloamides and N-nitrosamines; 

A Critical Review of Nitrogenous Disinfection Byproduct Formation Pathways. Environmental 

Science and Technology, 46:1:119.

Sheffer, P.J., J.E. Stout, M.M. Wagener, and R.R. Muder. 2005. Efficacy of new point-of-use 

water filter for preventing exposure to Legionella and waterborne bacteria. Infection Control, 33: 

S20-S25. 

Sidari, F.P., J.E. Stout, S. Duda, D. Grubb, and A. Neuner. 2014. Maintaining Legionella control 

in building water systems. Journal AWWA, 106(10): 24-32. 

Sidari, F.P., J.E. Stout, J.M. Vanbriesen, A.M. Bowman, D. Grubb, A. Neuner, M.M. Wagener, 

and V.L. Yu. 2004. Keeping Legionella out of water systems. Journal AWWA, 96(1): 111-119. 

Silk, B.J., M.R. Moore, M. Bergtholdt, R.J. Gorwitz, N.A. Kozak, M.M. Tha, E.W. Brown, J.L. 

Winchester, B.J. Labus, P. Rowley, J.P. Middaugh, B.S. Fields, and L.A. Hicks. 2012. Eight 

years of Legionnaires' disease transmission in travellers to a condominium complex in Las 

Vegas, Nevada. Epidemiology and Infection, 140(11): 1993-2002. 

Snyder, M.B., M. Siwicki, J. Wireman, D. Pohlod, M. Grimes, S. Bowman-Riney, and L.D. 

Saravolatz. 1990. Reduction in Legionella pneumophila through heat flushing followed by 

continuous supplemental chlorination of hospital hot water. Infectious Diseases, 162: 127-132. 

Spadaro, J.A., T.J. Berger, S.D. Barranco, S.E. Chapin, and R.O. Becker. 1974. Antibacterial 

effects of silver electrodes with weak direct current. Antimicrobial Agents and Chemotherapy, 

6(5): 637-642. 

States, S., J. Kuchta, W. Young, L. Conley, J. Ge, M. Costeloa, J. Dowling, and R. Wadowsky. 

1998. Controlling Legionella using copper-silver ionization. American Water Works Association.

90(9): 122-129. 

States, S.J., R.M. Wadowsky, J.M. Kuchta, R.S. Wolford, L.F. Conley, and R.B. Yee. 1990. 

Legionella in drinking water. In: Drinking Water Microbiology. G.A. McFeters, (ed.). p. 340-

367. New York, NY: Springer-Verlag.

Steinert, M., L. Emody, R. Amann and J. Hacker. 1997. Resuscitation of viable but 

nonculturable Legionella pneumophila Philadelphia JR32 by Acanthamoeba castellanii. Applied 

and Environmental Microbiology, 63(5): 2047-2053. 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 87 October 2015 

Storey, M.V., N.J. Ashbolt, and T.A. Stenström. 2004b. Biofilms, thermophilic amoeba and 

Legionella pneumophila – a quantitative risk assessment for distributed water. Water Science 

and Technology. 50(1): 77-82. 

Storey, M.V., J. Winiecka-Krusnell, N.J. Ashbolt, and T.A. Stenström. 2004a. The efficacy of 

heat and chlorine treatment against thermotolerant Acanthamoebae and Legionellae.

Scandinavian Journal of Infectious Diseases. 36(9): 656-662. 

Stout, J.E. and V.L. Yu. 1997. Legionellosis. New England Journal of Medicine, 337: 682-687. 

Stout, J.E. and V.L. Yu. 2003. Experiences of the first 16 hospitals using copper-silver ionization 

for Legionella control: implications for the evaluation of other disinfection modalities. Infection 

Control and Hospital Epidemiology. 24: 563-568. 

Stout, J.E., V.L. Yu, and M.G. Best. 1985. Ecology of Legionella pneumophila within water 

distribution systems. Applied and Environmental Microbiology. 49(1): 221-228. 

Stout, J.E., V.L. Yu, P. Muraca, J. Joly, N. Troup, and L.S. Tompkins. 1992. Potable water as a 

cause of sporadic cases of community-acquired Legionnaires’ disease. New England Journal of 

Medicine. 326: 151-155. 

Symons, J. M. 1978. Ozone, chlorine dioxide and chloramines as alternatives to chlorine for 

disinfection of drinking water. U.S. Environmental Protection Agency, Cincinnati, Ohio. 

Symons, J.M., J.K. Carswell, R.M. Clark, P. Dorsey, E.E. Geldreich, W.P. Heffernan, J.C. Hoff, 

O.T. Love, L.J. McCabe, and A.A. Stevens. 1977. Ozone, Chlorine Dioxide and Chloramines as 

Alternatives to Chlorine for Disinfection of Drinking Water. State-of-the-Art. Water Supply 

Research, Office of Research and Development. Cincinnati, Ohio. November 1977. 

Taylor, M., K. Ross, and R. Bentham. 2009. Legionella, protozoa, and biofilms: interactions 

within complex microbial systems. Microbial Ecology. 58: 538-547. 

Temmerman, R., H. Vervaeren, B. Noseda, N. Boon, and W. Verstraete. 2006. Necrotrophic 

growth of Legionella pneumophila. Applied and Environmental Microbiology, 72(6), 4323-4328. 

Thomas, V., T. Bouchez, V. Nicolas, S. Robert, J.F. Loret and Y. Levi. 2004. Amoebae in 

domestic water systems: resistance to disinfection treatments and implication in Legionella

persistence. Applied Microbiology, 97: 950-963. 

Thompson, C., J. Drago, B. Loeb, and G. Hunter. 2013. Forty Years of Ozone Experience 

Treating Municipal Water Supplies in the United States. Proc. 2013 Joint IOA/IUVA World 

Congress. 

Tobin, J.O., C.L. Bartlett, S.A. Waitkins, G.I. Barrow, A.D. Macrae, A.G. Taylor, R.J. Fallon, 

and F.R. Lynch. 1981a. Legionnaires’ disease: further evidence to implicate water storage and 

distribution systems as sources. British Medical Journal, 282: 573. 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 88 October 2015 

Tobin, J.O., R.A. Swann, and C.L. Bartlett. 1981b. Isolation of Legionella pneumophila from 

water systems: methods and preliminary results. British Medical Journal, 282: 515-517. 

Travis, T.C., E.W. Brown, L.F. Peruski, D. Siludjai, P. Jorakate, P. Salika, G. Yang, N.A. 

Kozak,, M. Kodani, A.K. Warner, C.E. Lucas, K.A. Thurman, J.M. Winchell, S. Thamthitiwat, 

and B.S. Fields. 2012. Survey of Legionella species found in Thai soil. International Journal of 

Microbiology, 2012: 1-4. 

Türetgen, I. 2004. Comparison of the efficacy of free residual chlorine and monochloramine 

against biofilms in model and full scale cooling towers. Biofouling. 20(2): 81-85. 

United States Environmental Protection Agency (USEPA). 1989a. Federal Register Notice

National Primary Drinking Water Regulations: Filtration, Disinfection, Turbidity, Giardia 

lamblia, Viruses, Legionella and Heterotrophic Bacteria; Final Rule. 54 FR 27486. (June 29, 

1989). Available online at: http://water.epa.gov/lawsregs/rulesregs/sdwa/swtr/upload/SWTR.pdf. 

United States Environmental Protection Agency (USEPA). 1989b. Integrated Risk Information 

System: Silver (CASRN 7440-22-4). Available online at: 

http://www.epa.gov/iris/subst/0099.htm. 

United States Environmental Protection Agency (USEPA). 1994. Drinking water criteria 

document for chloramines. ECAO-CIN-D002. 

United States Environmental Protection Agency (USEPA). 1996. Water Supply Guidance-90: 

State Alternative Technology Approval Protocol. Available online at:

http://water.epa.gov/lawsregs/guidance/sdwa/upload/wsg_90.pdf. 

United States Environmental Protection Agency (USEPA). 1998. Federal Register Notice

National Primary Drinking Water Regulations; Disinfectants and Disinfection Byproducts; Final 

Rule. 63 FR 69390. (December 16, 1998). Available online at: 

http://www.gpo.gov/fdsys/pkg/FR-1998-12-16/pdf/98-32887.pdf. 

United States Environmental Protection Agency (USEPA). 1999a. Legionella: Human health 

criteria document. EPA-822-R-99-001. 

United States Environmental Protection Agency (USEPA). 1999b. 25 years of the Safe Drinking 

Water Act: history and trends. EPA 816-R-99-007. 

United States Environmental Protection Agency (USEPA). 1999c. Alternative disinfectants and 

oxidants guidance manual. EPA 815-R-99-014. 

United States Environmental Protection Agency (USEPA). 1999d. Microbial and Disinfection 

Byproducts Rules simultaneous compliance guidance manual. EPA 815-R-99-015. 

United States Environmental Protection Agency (USEPA). 2001. Low pressure membrane 

filtration for pathogen removal: application, implementation and regulatory issues. EPA 815-C01-001. 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 89 October 2015 

United States Environmental Protection Agency (USEPA). 2005a. Economic analysis for the 

Final Stage 2 Disinfectants and Disinfection Byproducts Rule. EPA 815-R-05-010. 

United States Environmental Protection Agency (USEPA). 2005b. Membrane filtration guidance 

manual. EPA 815-R-06-009. 

United States Environmental Protection Agency (USEPA). 2006a. Hazard Analysis Critical 

Control Point (HACCP) strategies for distribution system monitoring, hazard assessment 

and control. 

United States Environmental Protection Agency (USEPA). 2006c. National Primary Drinking 

Water Regulations: Stage 2 Disinfectants and Disinfection Byproducts Rule; Final Rule. 71 FR 

388. (January 4, 2006). Available online at: http://www.gpo.gov/fdsys/pkg/FR-2006-01-

04/pdf/06-3.pdf. 

United States Environmental Protection Agency (USEPA). 2006d. Point-of-use or point-of-entry 

treatment options for small drinking water systems. EPA-815-06-010. 

United States Environmental Protection Agency (USEPA). 2006e. Ultraviolet disinfection 

guidance manual for the Final Long Term 2 Enhanced Surface Water Treatment Rule. EPA 815-

R-06-007. 

United States Environmental Protection Agency (USEPA). 2007. Simultaneous compliance 

guidance manual for the Long Term 2 and Stage 2 DBP Rules. EPA 815-R-07-017. 

United States Environmental Protection Agency (USEPA). 2009. Chloramines Q &A’s. EPA 

815-B-09-001. 

United States Environmental Protection Agency (USEPA). 2010. Comprehensive Disinfectants 

and Disinfection Byproducts Rules (Stage 1 and Stage 2): quick reference guide. EPA 816-F-10-

080. Available online at: http://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=P100C8XW.txt. 

United States Environmental Protection Agency (USEPA). 2012. The Third Unregulated 

Contaminants Monitoring Rule (UCMR3): Fact Sheet for Assessment Monitoring of List 1 

Contaminants. EPA 815-F-12-003. Available online at: 

http://water.epa.gov/lawsregs/rulesregs/sdwa/ucmr/ucmr3/upload/UCMR3_FactSheet_List1.pdf. 

United States Environmental Protection Agency (USEPA). 2014a. Analytical methods approved 

for drinking water compliance monitoring under the Disinfection Byproduct Rules. EPA 815-B14-004. Available online at:

http://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P100J7AR.txt. 

United States Environmental Protection Agency (USEPA). 2014b. NDMA Fact Sheet. Available 

online at: http://www2.epa.gov/sites/production/files/2014-

03/documents/ffrrofactsheet_contaminant_ndma_january2014_final.pdf. 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 90 October 2015 

van Heijnsbergen, E., A.M. de Roda Husman, W.J. Lodder, M. Bouwknegt, A.E. Docters van 

Leeuwen, J.P. Bruin, S.M. Euser, J.W. den Boer, and J.A.C. Schalk. 2014. Viable Legionella 

pneumophila bacteria in natural soil and rainwater puddles. Applied Microbiology. 117(3): 882-

890. 

Vonberg, R.P., D. Sohr, J. Bruderek, and P. Gastmeier. 2008. Impact of a silver layer on the 

membrane of tap water filters on the microbiological quality of filtered water. BMC Infectious 

Diseases. 8: 133. 

Wadowsky R.M., R. Wolford, A.M. McNamara, and R.B. Yee. 1985. Effect of temperature, pH 

and oxygen level on the multiplication of naturally occurring Legionella pneumophila in potable 

water. Applied and Environmental Microbiology. 49(5): 1197–1205. 

Wadowsky, R.M. and R.B. Yee. 1983. Satellite growth of Legionella pneumophila with an 

environmental isolate of Flavobacterium breve. Applied and Environmental Microbiology.

46(6): 1447–1449. 

Wadowsky, R. M., R. B. Yee, L. Mezmar, E. P. Wing, and J. N. Dowling. 1982. Hot water 

systems as sources of Legionella pneumophila in hospital and non-hospital plumbing fixtures. 

Applied and Environmental Microbiology. 43: 1104-1110. 

Wallensten, A., I. Oliver, K. Ricketts, G. Kafatos, J. M. Stuart, and C. Joseph. 2010. Windscreen 

wiper fluid without added screenwash in motor vehicles: a newly identified risk factor for 

Legionnaires’ disease. European Journal of Epidemiology. 25(9): 661-665. 

Wang, H., S. Masters, Y. Hong, J. Stallings, J.O. Falkinham III, M.A. Edwards, and A. Pruden. 

2012. Effect of disinfectant, water age and pipe material on occurrence and persistence of 

Legionella, mycobacteria, Pseudomonas aeruginosa and two amoebas. Environmental Science 

and Technology. 46: 11566-11574. 

Washington State Department of Health (WSDOH). 2009. Water system design manual. DOH 

331-123. 

Weintraub, J.M., B. Flannery, D.J. Vugia, L.B. Gelling, J.J. Salerno, V.A. Stevens, C.E. Rose, 

R.E. Besser, B.S. Fields, M.R. Moore, and M.J. Conroy. 2008. Legionella reduction after 

conversion to monochloramine for residual disinfection. Journal AWWA. 100(4): 129-139. 

Whiley, H. and R. Bentham. 2011. Legionella longbeachae and Legionellosis. Emerging 

Infectious Diseases. 17(4): 579-583. 

Whiley, H., A. Keegan, H. Fallowfield, and R. Bentham. 2014. Detection of Legionella, L. 

pneumophila and mycobacterium avium complex (MAC) along potable water distribution 

pipelines. International Journal of Environmental Research and Public Health. 11: 7393-7405. 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 91 October 2015 

Williams, M.M., C.R. Armbruster and M.J. Arduino. 2013. Plumbing of hospital premises is a 

reservoir for opportunistically pathogenic microorganisms: a review. Biofouling: The Journal of 

Bioadhesion and Biofilm Research. 29(2): 147-162. 

Wilson, B.R., P.F. Roessler, E. Van Dellen, M. Abbaszadegan, and C.P. Gerba. 1992. Coliphage 

MS-2 as a UV disinfection efficacy test surrogate for bacterial and viral pathogens. In 

Proceedings of Water Quality Technology Conference. Denver, Colo., American Water Works 

Association. 

World Health Organization (WHO). 1996. Silver in Drinking Water: Background document for 

development of WHO Guidelines for Drinking-water Quality. WHO/SDE/WSH/03.04/14. 

Geneva, Switzerland.

World Health Organization (WHO). 2004. Monochloramine in drinking-water; Background 

document for development of WHO Guidelines for Drinking-water Quality. 

WHO/SDE/WSH/03.04/83. Geneva, Switzerland. 

World Health Organization (WHO). 2005. Water Safety Plans. Managing drinking-water quality 

from catchment to consumer. WHO/SDE/WSH/05.06. Geneva, Switzerland. 

World Health Organization (WHO). 2011. Water safety in buildings. Geneva, Switzerland. 

Wright, H., D. Gaithuma, M. Heath, C. Schulz, T. Bogan, A. Cabaj, A. Schmalweiser, M. 

Schmelzer, and J. Finegan-Kelly. 2012. UV disinfection knowledge base. Denver, Colo., Water 

Research Foundation. 

Yahya, M.T., S.M. Kutz, L.K. Landeen, and C.P. Gerba. 1989. Swimming pool disinfection: an 

evaluation of the efficacy of copper/silver ions. Environmental Health. 51(5): 282-285. 

Yee, R.B. and Wadowsky, R.M., 1982. Multiplication of Legionella pneumophila in Unsterilized 

Tap Water. Applied and Environmental Microbiology, 43(6): 1330. 

Yokoi, H., M.Y. Embutsu, and K. Waseda. 2006. Study on the introduction of hazard analysis 

and critical control point (HACCP) concept of the water quality management in water supply 

systems. Water Science and Technology. 53(4-5): 483-492. 

Yu, W., B. Azhdar, D. Anderson, T. Reitberger. J. Hassinen, T. Hjertberg, U.W. Gedde. 2011. 

Deterioration of polyethylene pipes exposed to water containing chlorine dioxide. Polymer 

Degradation and Stability. 96: 790-797. 

Yu, V.L., J.F. Plouffe, M.C. Pastoris, J.E. Stout, M. Schousboe, A. Widmer, J. Summersgill, T. 

File, C.M. Heath, D.L. Paterson, and A. Chereshsky. 2002. Distribution of Legionella species 

and serogroups isolated by culture in patients with sporadic community-acquired legionellosis: 

an international collaborative survey. Infectious Diseases. 186: 127–128. 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 92 October 2015 

Zevenhuizen, L.P., J. Dolfing, E.J. Eshuis, and I.J. Scholten-Koerselman. 1979. Inhibitory effects 

of copper on bacteria related to free ion concentration. Microbial Ecology. 5: 139-146. 

Zhang, Z., C. McCann, J. Hanrahan, A. Jencson, D. Joyce, S. Fyffe, S. Piesczynski, R. Hawks, J. 

E. Stout, V.L. Yu, and R.D. Vidic. 2009. Legionella control by chlorine dioxide in hospital water 

systems. Journal AWWA, 101(5): 117-127. 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 93 October 2015 

A Appendix

A.1 Elements of Hazard Analysis and Critical Control Points (HACCP)

HACCP is based on an engineering concept of failure, mode and effects analysis. It has five 

initial steps followed by seven main principles (Mortimore and Wallace, 2001). 

The five initial steps are below (FAO, 1998): 

• Step 1: Assemble HACCP team

• Step 2: Describe the product

• Step 3: Identify intended use 

• Step 4: Construct a process flow diagram 

• Step 5: Verification of the process flow diagram 

The seven principles include the following: 

• Principle 1: Conduct a hazard analysis

• Principle 2: Determine the critical control points 

• Principle 3: Establish critical limit(s)

• Principle 4: Establish a system to monitor control of critical control points

• Principle 5: Establish corrective actions

• Principle 6: Validate/verify HACCP plan

• Principle 7: Establish documentation and recordkeeping procedures 

The first step, assembling the HACCP team, is best completed by bringing together a multidisciplinary team. The team may consist of a lead coordinator along with team members 

representing different areas of expertise or responsibilities for managing the building water 

system. This can include but is not limited to building managers, building water system 

operators, engineers, maintenance staff, laboratory managers, plumbing experts, public health 

risk assessors, financial experts and environmental health specialists. In some cases, the HACCP 

team may include external experts (WHO, 2011; Mortimore and Wallace, 2001). The inclusion 

of staff with a broad range of expertise helps to ensure that all priority risks will be identified and 

decisions on control measures will be practical to implement (Martel et al., 2006). The roles 

(e.g., task manager, trainer, lead reviewer), responsibilities (e.g., collecting samples) and 

expertise (e.g., backflow prevention, water treatment) of each team member are usually

summarized in the HACCP plan. 

The second step involves describing the product, in this case the building water. The description 

usually includes water characteristics such as pH, storage conditions, temperatures, current 

treatment, and source water information (e.g., the type of treatment that was applied to the water 

prior to it reaching the building service connection, how/where the water was stored and 

distributed throughout the PWS, and standards the water must meet before it reaches the service 

connection) (USEPA, 2006a). 

The third step is to identify the intended use(s) of the water. Examples can include drinking, 

bathing, swimming, cleaning, laundry, flushing toilets, building heating, cooling and fire 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 94 October 2015 

protection. These intended uses can help indicate the different routes of exposures such as 

consumption, inhalation and dermal absorption (WHO, 2005). The intended uses may vary 

depending on the type of facility containing the building water system. For example, a hospital 

might have additional water uses that a hotel or condominium would not have, and vice versa. 

The population using the water will also vary among different types of facilities (e.g., a nursing 

home will most likely have a larger elderly and immunocompromised population than a hotel). 

The fourth step is to construct a process flow diagram. This diagram describes in detail the 

building water system from the point where the water is first received (the building service 

connection) to where the water meets its intended uses, such as at the tap for consumption, 

showering, flushing toilets, or a hot tub. This diagram will include all aspects of the building 

water system, such as hot water networks, cold water networks, equipment installed at point-ofuse (e.g., filters), backflow prevention assemblies, and cross connections (direct and indirect). 

Descriptions of the water at different points in the system are also usually included, such as 

temperatures in the hot and cold water networks, pressures at backflow prevention devices, and 

water age throughout the system. Water uses and patterns are also important to include within the 

process flow diagram, including intended and unintended uses (WHO, 2011). 

The fifth step is to verify the process flow diagram. This refers to an on-site visual inspection of 

the entire building water system during initial development of the HACCP plan and periodic 

review after construction or maintenance work. The periodic review occurs during various times 

to ensure accuracy during all operational processes. Not only does this step ensure all of the 

different operational aspects of the building water system are accounted for, it also confirms the 

different uses and use patterns in the process flow diagram (FAO, 1998). During the on-site 

inspection, the HACCP team confirms that the building water system meets applicable codes 

(Rosenblatt and McCoy, 2014). 

After the five initial steps have been completed, the seven principles of HACCP are initiated. 

The first principle of HACCP involves conducting a hazard analysis to identify and prioritize 

possible hazards in a particular building water system and to identify appropriate control 

measures. Hazards within a building water system can be biological, chemical, radiological or 

physical. These can occur at many points throughout the entire building water system (WHO, 

2011; FAO, 1998). An example of a physical hazard in a building water system is scalding due 

to hot water or steam (Rosenblatt and McCoy, 2014). An example of chemical exposure is lead 

leaching from pipework, and an example of microbial exposure is Legionella growing in 

biofilms. Along with identifying hazards, it is important to specify how likely the contaminant or 

hazard is to occur, the different control measures put in place for the identified hazard, and the 

severity of consequences of the hazard occurring (Martel et al., 2006; USEPA, 2006a). 

The second principle of HACCP is identification of critical control points (FAO, 1998). Critical 

control points are specific points in the building water system that are essential to preventing and 

eliminating hazards and where controls can be applied (new or controls currently in place) (FAO, 

1998). Decision trees can be useful tools in determining which control points are critical 

(Mortimore and Wallace, 2001). Examples of critical control points in a building water system 

can include hot water heaters, the location where disinfection is applied, locations where 

backflow prevention assemblies are installed or should be installed, the location of POU

controls, and the points at which routine flushing is conducted. 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 95 October 2015 

The third HACCP principle is establishment of critical limits for the control measures employed 

at each critical control point. These critical limits are measurable criteria that separate safe from 

potentially unsafe conditions (WHO, 2011; Mortimore and Wallace, 2001). Examples of critical 

limits in a building water system can include temperature ranges for a hot water heater, 

temperature ranges for hot and cold water lines, disinfectant levels at the point of application or 

at distal taps, and the frequency for changing POU filters. 

The fourth HACCP principle is identification of monitoring procedures for each critical limit set 

for each control point (Mortimore, 2001; WHO, 2011). The monitoring procedures describe what 

parameter is being monitored, the monitoring frequency and location, monitoring methods, and 

reporting and recordkeeping procedures. According to FAO (1998) the procedures should also 

identify staff responsible for each aspect of the monitoring procedures, such as which staff are

responsible for sample collection and analysis. 

The fifth HACCP principle is the establishment of corrective actions. When a critical limit is 

exceeded, the corrective action procedure will be carried out to restore values to the expected 

range. The procedure will also include processes for determining the cause of the exceedance to 

ensure it does not recur (FAO, 1998). For example, if the disinfectant residual at distal taps is too 

low, the corrective action may include increasing the chemical dosage rate or boosting it at 

another location in the system. Other corrective action procedures for managing critical limits 

within building water systems could include maintenance on equipment, inspecting chemical 

feed pumps, inspecting boiler controls, preventing the use of contaminated water (e.g., providing 

bottled water, shutting off the tap, using an alternative water source), superheating the system, 

and flushing the piping system (WHO, 2011). Similar to monitoring procedures described under 

the fourth principle, corrective action procedures identify the staff responsible for each task. 

The sixth HACCP principle is establishment of verification and validation procedures. The 

validation step ensures the system is safe from hazards and that the HACCP plan is effectively 

controlling for hazards. Validation may include monitoring physical, chemical or 

microbiological parameters, as well as review of clinical surveillance data. Validation can also 

help identify unnecessary and ineffective control measures (Rosenblatt and McCoy, 2014; 

Mortimore, 2001; FAO, 1998). The verification step ensures the HACCP plan is working 

correctly and provides evidence that the HACCP plan is being implemented as intended. 

Verification activities may involve a supervisor checking that staff members have performed 

monitoring, maintenance and recordkeeping tasks outlined in the HACCP plan. 

The seventh HACCP principle is the establishment of documentation and recordkeeping. It is 

imperative to the HACCP process that complete and accurate records are maintained (FAO, 

1998). Recordkeeping allows the HACCP team to track the system’s performance of the HACCP 

plan as well as the performance of control measures (USEPA, 2006a). In the event that a water 

system experiences a waterborne disease outbreak or another water quality event that could 

affect public health, historical water quality data and system records can be helpful to prove due 

diligence (i.e., that appropriate steps were taken to control known hazards). 
Draft – Technologies for Legionella Control: 

Scientific Literature Review 96 October 2015 

A.2 Elements of a Water Management Program

Source: ASHRAE, 2015.
Draft – Technologies for Legionella Control: 

Scientific Literature Review 97 October 2015 

A.3 Elements of Water Safety Plan 

Source: WHO, 2005.