Chapter 14—Residential Swimming Pools and Spas

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-1

Child-proofing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-1

Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-2

Public Health Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-2

Diseases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-3

Injuries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-3

Water Testing Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-3

Disinfection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-4

Content Turnover Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-4

Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-5

High-rate Sand Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-5

Cartridge Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-5

Diatomaceous Earth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-5

Filter Loading Rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-5

Disinfectants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-5

Effect of pH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-6

Chlorine Disinfectants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-6

Pool Water Hardness and Alkalinity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-8

Liquid Chemical Feeders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-9

Positive Displacement Pump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-9

Erosion and Flow-through Disinfectant Feeders . . . . . . . . . . . . . . . . . . . . . .14-10

Spas and Hot Tubs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-10

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-11

Additional Sources of Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-11

Figure 14.1. Pool Cover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-2

Figure 14.2. Typical Home Pool Equipment System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-5

Table 14.1. Pool Water Quality Problem Solving . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-7

Table 14.2. pH Effect on Chlorine Disinfection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-8

Table 14.3. Chlorine Use in Swimming Pools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-8

Table 14.4. Swimming Pool Operating Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-9

Table 14.5. Spa and Hot Tub Operating Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-11

Healthy Housing Reference Manual 1

Contents
Chapter 14: Residential Swimming Pools and Spas

“Most people assume if their young child falls into the pool,

there will be lots of splashing and screaming, and plenty of

time to react. In reality, a child slips into the water and

often goes under the surface. These drownings can happen

quickly and silently-without warning.”

Hal Stratton, Chair 

U.S. Consumer Product Safety Commission,

2002–Present

Introduction

Swimming is one of the best forms of exercise available

and having a residential swimming pool also can provide

much pleasure. Nevertheless, it takes a great deal of work

and expense to make and keep the pool water clean and

free of floating debris. Without a doubt, a properly

maintained and operated pool is quite rewarding. Home

pools, however, are sometimes referred to as attractive

nuisances or hazards. It is essential to be able to evaluate

the risks associated with a pool. A regulatory agent or

consultant must understand the total engineered pool

system and be capable of identifying all equipment,

valves, and piping systems. The piping system for a pool

should be color-coded to assist the pool operator or the

owner to determine the correct way to operate the

swimming pool. The specific goal is to protect the

owners, their families, and others who may be attracted

to a residential pool. 

Residential pools and spas should provide clean, clear water;

water free of disease agents; and a safe recreational

environment. In addition, residential pools and spas

should have effective, properly operating equipment and

effective maintenance and operation.

Childproofing 

Although it seems obvious, close supervision of young

children is vital for families with a residential pool. A

common scenario is a young child leaving the house without

the parent or caregiver realizing it. Children are drawn to

water, and they can drown even if they know how to swim.

All children should be supervised at all times while in

and around a pool. 

The key to preventing pool tragedies is to provide layers

of protection. These layers include limiting pool access, using

pool alarms, closely supervising children, and being prepared

in case of an emergency. The U.S. Consumer Product Safety

Commission (CPSC) offers these tips to prevent drowning: 

• Fences and walls should be at least 4 feet high

and installed completely around the pool. The

fence should be no more than 2 inches above

grade. Openings in the fence should be a

maximum of 4 inches. A fence should be difficult

to climb over. 

• Fence gates should be self-closing and selflatching. The latch should be out of a small

child’s reach. The gate should open away from

the pool; the latch should face the pool.

• Any doors with direct pool access should have an

audible alarm that sounds for 30 seconds. The

alarm control must be a minimum of 54 inches

high and reset automatically. 

• If the house forms one side of the barrier to the

pool, then doors leading from the house to the

pool should be protected with alarms that

produce a sound when a door is opened.

• Young children who have taken swimming

lessons should not be considered “drown proof”;

young children should always be watched

carefully while swimming.

• A power safety cover-a motor-powered barrier

that can be placed over the water area-can be

used when the pool is not in use.

• Rescue equipment and a telephone should be

kept by the pool; emergency numbers should be

posted. Knowing cardiopulmonary resuscitation

(CPR) can be a lifesaver.

• For aboveground pools, steps and ladders should

be secured and locked or removed when the pool

is not in use.

• Babysitters should be instructed about potential

hazards to young children in and around

swimming pools and their need for constant

supervision.

• If a child is missing, the pool should always be

checked first. Seconds count in preventing death

or disability.

Healthy Housing Reference Manual 14-1
• Pool alarms can be used as an added precaution.

Underwater pool alarms can be used in

conjunction with power safety covers. CPSC

advises consumers to use remote alarm receivers so

the alarm can be heard inside the house or in

other places away from the pool area.

• Toys and flotation devices should be used in pools

only under supervision; they should not be used

in place of supervision.

• Well-maintained rescue equipment (including a

ring buoy with an attached line and/or a

shepherd’s crook rescue pole should be kept by the

pool.

• Emergency procedures should be clearly written

and posted in the pool area.

• All caregivers must know how to swim, know how

to get emergency help, and know CPR.

• Children should be taught to swim (swimming

classes are not recommended for children under

the age of 4 years) and should always swim with a

buddy.

• Alcohol should not be consumed during or just

before swimming or while supervising children.

• To prevent choking, chewing gum and eating

should be avoided while swimming, diving, or

playing in water.

• Water depth should be checked before entering a

pool. The American Red Cross recommends 9 feet

as a minimum depth for diving and jumping.

• Rules should be posted in easily seen areas. Rules

should state “no running,” “no pushing,” no

drinking,” and “never swim alone.” Be sure to

enforce the rules.

• Tables, chairs, and other objects should be placed

well away from the pool fence to prevent children

from using them to climb into the pool area.

• When the pool is not in use, all toys should be

removed to prevent children from playing with or

reaching for them and unintentionally falling into

the water.

• A clear view of the pool from the house should be

ensured by removing vegetation and other

obstacles that block the view.

Hazards 

Numerous issues need to be considered before building

residential pools: location of overhead power lines,

installation and maintenance of ground fault circuit

interruptors, electrical system grounding, electrical wiring

sizing, location of the pool, and type of vegetation near

the pool. The commonly used solar covers that rest on the

surface of the pool and amplify sunlight do an excellent

job of increasing the pool temperature, and they also

increase the risk for drowning. If children or pets fall in

and sink below the cover, it can be nearly impenetrable if

they attempt to surface under it. 

Winterizing the pool also can be hazardous. The pool

water in most belowground pools is seldom drained

because of groundwater pressure that can damage the

structure of the pool. Therefore, water in most home

pools is only lowered below the frost line for winter

protection. In these cases, a pool cover is installed to keep

debris and leaves from filling the pool in the winter

months. The pool cover becomes an excellent mosquitobreeding area before the pool is reopened in the spring

because of the decomposing vegetation that is on the pool

cover, the rain that accumulates on the top of the pool

cover during the winter, and the eggs laid on the pool

cover in early fall and early spring. The cover also

provides ideal conditions for mosquitoes to breed:

stagnant water, protection from wind that can sink

floating eggs, the near absence of predators, and warm

water created by the pool cover collecting heat just below

the surface (Figure 14.1).

Public Health Issues 

Current epidemiologic evidence indicates that correctly

constructed and operated swimming pools are not a

14-2 Residential Swimming Pools and Spas

Figure 14.1. Pool Cover
major public health problem. They are preferable to

bathing beaches because of the engineered controls

designed into pools. Poorly designed or operated pools,

however, can be major public health hazards. Data from

CDC between 1999 and 2000 show that 59 disease

outbreaks from 23 states were attributed to recreational

water exposure and affected an estimated 2,093 people.

Of the 59 recreational outbreaks, 44 (74.6%) were of

known infectious etiology. Of the 36 outbreaks involving

gastroenteritis, 17 (47.2%) were caused by parasites;

9 (25.0%) by bacteria; 3 (8.3%) by viruses; 1 (2.8%) by a

combination of parasites and bacteria, and the remaining

6 (16.7%) were of unknown cause. Of the

23 nongastroenteritis-related recreational outbreaks, seven

were attributed to Pseudomonas aeruginosa, four to freeliving amoebae, one to Leptospira species, one to

Legionella species, and one to bromide. Sixteen of the

17 parasitic recreational water outbreaks involving

gastroenteritis; nine (24.3%) were outbreaks of dermatitis;

and six (16.2%) were caused by Cryptosporidium parvum.

The seventeenth outbreak was caused by Giardia lamblia

(intestinalis). In 1999, an outbreak of Campylobacter

jejuni was associated with a private pool that did not have

continuous chlorine disinfection and reportedly had

ducks swimming in the pool [1].

Diseases

• Intestinal diseases: Escherichia coli O157:H7,

typhoid fever, paratyphoid fever, amoebic dysentery,

leptospirosis, cryptosporidiosis (highly chlorine

resistant), and bacillary dysentery can be a

problem where water is polluted by domestic or

animal sewage or waste. Swimming pools have

also been implicated in outbreaks of leptospirosis.

• Respiratory diseases: Colds, sinusitis, and septic

sore throat can spread more readily in swimming

areas as a result of close contact, or improperly

treated pool water, coupled with lowered

resistance because of exertion.

• Eye, ear, nose, throat, and skin infections: The

exposure of delicate mucous membranes, the

movement of harmful organisms into ear and

nasal passages, the excessive use of watertreatment chemicals, and the presence of harmful

agents in water can contribute to eye, ear, nose,

throat, and skin infections. Close physical contact

and the presence of fomites (such as towels) also

help to spread athlete’s foot, impetigo, and dermatitis.

Injuries

Injuries and drowning deaths are by far the greatest problem

at swimming pools. Lack of bather supervision is a prime

cause, as is the improper construction, use, and maintenance

of equipment. Injuries include evisceration, electrocution,

entrapment, and entanglement. Some particular problem

areas include the following:

• lose or poorly located diving board,

• slippery decks or pool bottoms,

• poorly designed or located water slides,

• projecting or ungrated pipes and drains that can

catch hair or body parts,

• drain grates of inadequate size,

• improperly installed or maintained electrical

equipment, and 

• improperly vented chlorinators and mishandled

chlorine materials.

Water Testing Equipment

It is essential that correct equipment be used and maintained

for assessing the water quality of both swimming pools

and spas. The operators of pool and spas need to monitor

a wide range of chemicals that influence pool operations

and water quality. Their equipment should test for chlorine,

bromine, pH, alkalinity, hardness, and cyanuric acid build

up. The chlorine should be measurable at a range of 0 to

10 parts per million (ppm). Water pH levels should be

accurately measured with an acid or base test. A kit to

check pool chemical levels usually includes N,N-diethylp-phenylene-diamine (DPD) tablet tests for free and total

chlorine, and other one-step tablet tests for pH, total

alkalinity, calcium hardness, and cyanuric acids. The

homeowner should determine acid or base demand using

an already reacted pH sample in dropper bottles. Paper

test strips with multiple tests (including chlorine, bromine,

and pH) are also available, but the reliability of these tests

varies greatly. If used, they should be kept fresh, protected

from heat and moisture, and checked against other test

systems periodically if water quality problems persist.

Swimming pools are engineered systems, with demanding

safety and sanitary requirements that result in rather

sophisticated design standards and water treatment

systems. The size, shape, and operating system of the pool

is based on the following considerations:

Healthy Housing Reference Manual 14-3
• the intended use of the pool and the maximum

expected bather loading;

• the selection of skimmers, scuppers, or gutters,

depending on the purpose, size, and shape of the

pool; 

• the recirculation pump, whose horsepower and

impeller configuration are based on the distance,

volume, and height of the water to be pumped; 

• the filters, which are sized on the volume of water

to be treated and the maximum gallons (liters) of

water per minute that can be delivered by the

pump and the type of filter media selected; and 

• the chemical feeder sizes and types, which are

based on the chemicals used, total quantity of the

water in the system, expected use rates, and

external environmental factors, such as quantity of

sunlight and wind that affect the system.

Disinfection 

The length of time it takes to disinfect a pool depends,

for example, on the type of fecal accident and the

chlorine levels chosen to disinfect the pool. If a fecal

accident is a formed stool, the faollowing chlorine levels

will determine the times needed to inactivate Giardia:

Chlorine Levels (ppm) Disinfection Time

1.0 45 minutes

2.0 25 minutes

3.0 19 minutes

These times are based on a 99.9% inactivation of Giardia

cysts by chlorine, pH 7.5, and 77°F (25°C). The times

were derived from the EPA LT1ESWTR Disinfection

Profiling and Benchmarking Technical Guidance Manual

[2]. These times do not take into account “dead spots”

and other areas of poor pool water mixing.

If the fecal accident is diarrhea, the following chlorine

levels will determine the times needed to inactivate

Cryptosporidia:

Chlorine Levels (ppm) Disinfection Time

1.0 6.7 days 

10.0 16 hours

20.0 8 hours

A CT value is the concentration (C) of free available

chlorine in parts per million (ppm) multiplied by the

time (T) in minutes (CT value = C×T ). The CT value

for Giardia is 45 and the value for Cryptosporidia is 9,600. If

a different chlorine concentration or inactivation time is

used, CT values must remain the same. For example, to

determine the length of time needed to disinfect a pool at

15 ppm after a diarrheal accident, the following formula

is used: C×T = 9,600. Solve for time: T= 9,600÷15 ppm

= 10.7 hours. It would, thus, take 10.7 hours to inactivate

Cryptosporidia at 15 ppm. You can do the same for

Giardia by using the CT of 45.

CDC has Web sites that contain excellent information

about safe swimming recommendations, recreational

water diseases, and disinfection procedures for fecal

accidents [3,4].

Content Turnover Rate

The number of times a pool’s contents can be filtered

though its filtration equipment in a 24-hour period is the

turnover rate of the pool. Because the filtered water is

diluted with the nonfiltered water of the pool, the

turbidity continually decreases. Once the pool water has

reached equilibrium with the sources of contamination, a

6-hour turnover rate will result in 98% clarification if the

pool is properly designed. A typical-use pool should have

a pump and filtration system capable of pumping the

entire contents of the pool though the filters every 6 hours. To

determine compliance with this 6-hour turnover standard,

the following formula is used:

Turnover rate = pool volume (gallons)/

flow rate×60 (minutes in hour)

Following is a sample calculation of the pool content

turnover rate using the rate of flow reading from the flow

meter:

Turnover rate = 90,000 (gallons in pool)/

180 gallons per minute×60 (minutes in hour)

8.3-hour turnover rate = 90,000 (pool volume in

gallons)/10,800

The above pool would not meet the required turnover

rate of 6 hours. The cause could be improperly sized

piping or restrictions in the piping, an undersized pump,

or undersized or clogged filters. This turnover rate would

probably result in cloudy water if the pool is used at the

normal bather load. The decreased circulation would also

make it difficult for the disinfecting equipment to meet

the required levels.

14-4 Residential Swimming Pools and Spas
Filters

Pool filters are not designed to remove bacteria, but to

make the water in the pool clear. Normal tap water looks

quite dingy if used to fill a pool and, in some cases, the

bottom of the pool is not visible. The maximum turbidity

level of a pool should be less than 0.5 nephelometric

turbidity units. Pool filters should be sized to ensure that

the complete contents of the pool pass through the filter

once every 6 hours. Home pools typically use one of three

types of filters.

High-rate Sand Filters 

High-rate sand filters were introduced more than 30 years

ago and reduced the size of the conventional sand filter by

80%. The sand filter is the most popular filter on the

market. High-rate sand filters use a silica sand that has

been strained to give it a uniform size. It is referred to as

pool-grade sand #20 silica. The sand is normally

0.45 millimeters (mm) to 0.55 mm in diameter. As water

passes through the filter, the sharp edges of the sand trap

the dirt from the pool water. When the backpressure of

the filter increases to 3 to 5 psi, the filter needs to be

cleaned. This is usually accomplished by reversing the

flow of the water through the filter and flushing the dirt

out the waste pipe until the water being discharged

appears clear. These filters perform best when used at

pressure levels below 15 to 20 gallons per minute,

depending on the manufacturer of the filter.

Cartridge Filters

Cartridge filters have been around for many years, but

only recently have gained in popularity in the pool

industry. They are similar to the filter on a car engine.

The water is passed through the cartridge and returned to

the pool. When the pressure of a cartridge filter increases

approximately 5 psi, the pump is turned off; and the top

of the filter is removed. The cartridge is removed and

either discarded and replaced or, in some cases, washed.

Diatomaceous Earth 

Diatomaceous earth (DE) is a porous powder made from

the skeletons of billions of microscopic animals that were

buried millions of years ago. There are two primary types

of DE filters, but they both work the same way. Water

comes into the filter, passes through the DE, and is

returned to the pool. If properly sized and operated, DE

filters are considered by some to provide the highest

quality of water. They are capable of filtering the smallest

particle size of all the filter types. It is usually adequate to

change the DE once every 30 days. However, if your pool

water is very dirty, it is not uncommon to change it

3–4 times a day until the water is clear. The frequency of

backwashing will depend on many factors, including the

size of your filter, flow rate of your plumbing, and the

bather load in your pool. When the pressure reading on

the filter reaches the level set by the manufacturer’s

manual, it will be ready for backwashing. 

Filter Loading Rates

The specification plate on the side of approved residential

or commercial swimming pool filters contains such

information as the manufacturer, type of filter, serial

number, surface area, and designed loading rate. Knowing

the surface area of the filter permits calculation of the

number of gallons flowing through the filter per minute.

An excessive flow rate can push the media into the pool

or force pool solids and materials thought the media,

resulting in turbid water. Figure 14.2 shows a typical

home pool treatment system. Regulations typically specify

how much water can be filtered through the various types

of pool filtration systems. 

Disinfectants

Many disinfectants are used in pools and spas around the

world, including halogen-based compounds (chlorine,

bromine, iodine), ozone, and ultraviolet light with

hydrogen peroxide. Those used most often are chlorine,

bromine, and iodine, and each has advantages and limitations.

Healthy Housing Reference Manual 14-5

Figure 14.2. Typical Home Pool Equipment System
Chlorine—Pools can be disinfected with chlorinereleasing compounds, including hypochlorite salt

compounds. Calcium hypochlorite is inexpensive and

popular for cold-water pools, but not suitable for hot

pools and spas because it will promote scaling on heat

exchangers and piping. Chlorine levels can be rapidly

reduced with high use and regular checks should be made

to ensure maintenance of disinfection. Some adjustment

of pH is required for most forms of chlorine disinfection.

When chlorine gas is used, a fairly high alkalinity needs

to be maintained to remove the acid formed during

dosing [5]. Sodium hypochlorite is a liquid chlorine, and

has a pH of 13, causing a slight increase in the pH of the

pool water, which should be adjusted with an acidic

mixture. The sun’s rays will degrade sodium hypochlorite.

Chlorinated isocyanate is available in three formsgranular, tablet, and stick. The granular form contains

55%–62% available chlorine and the stick and tablet

form contain 89% available chlorine [6].

Bromine—Bromine needs to be used at levels twice those

of chlorine to achieve similar disinfection. Bromine is

available as the sodium or potassium salts. In the presence

of ammonia, bromine rapidly forms relatively unstable

ammonia bromamines that possess disinfection

efficiencies comparable to that of free bromine. It is also

unnecessary to destroy ammonia bromamines because

they do not produce irritating odors [5].

Iodine—Potassium iodide is a white, crystal chemical.

This chemical needs an oxidizer, such as hypochlorite, to

react with organic debris and bacteria. Iodine does not

react with ammonia, hair, or bathing suits, or cause eye

irritation, but it can react with metals, producing greenishcolored pool water [6].

Ozone—Ozone is a very powerful oxidant and is effective

against viruses. It can only be generated at the point of

use and commercial generation units are safe for use.

Ozone dosing is only practical where there is water

circulating off-pool because adequate ozone-water mixing

is essential for maximum oxidation. Ozone generators

may be of the ultraviolet lamp or corona discharge type.

The ultraviolet lamp efficiency reduces with time and the

lamp and associated activated charcoal filter will need

replacement [5].

Ultraviolet Light—Ultraviolet light, like ozone, is

sometimes used for off-pool water disinfection.

Ultraviolet light has no effect on pH or color and has

little effect on the chemical composition of the water.

However, color, turbidity, and chemical composition of

the water can interfere with ultraviolet light transmission.

The water must be adequately treated before ultraviolet

light exposure. Hydrogen peroxide is often used for this

purpose as it is relatively safe in low concentrations, is

nonflammable, and produces oxygen and water as end

products. For the ultraviolet light plus hydrogen peroxide

system to be effective, it must operate 24 hours a day.

Ultraviolet light disinfection is not pH dependent, but

the addition of hydrogen peroxide results in slightly acidic

conditions [5].

Silver-copper Ionization—Sanitizing can be

accomplished by using an ionizing unit that introduces

silver and copper ions into the water by electrolysis, or by

passing an electric current through a silver and copper

electrode. The limiting factors in using this system in the

pool and spa are cost, slow bactericidal action, and

potentially high contaminant levels caused by bather

loads. Also, black spots can form on pool surfaces if the

proper parameters of water chemistry are not maintained.

An approved chemical disinfectant must be used with an

ionizing unit [6].

The effective use of halogen disinfectants is based on the

pH, hardness, and alkalinity of the water. Improper pH,

hardness, and alkalinity levels in the pool can render high

levels of disinfectant useless in killing disease-causing

organisms. Table 14.1 summarizes water-quality problems

that affect pools and suggests corrective actions. 

Effect of pH 

The ideal pH to avoid eye irritation is 7.3. Bacteria- or

algae-killing effectiveness is improved with an even lower

pH. National standards typically recommend a range of

7.2 to 7.6, which is cost-effective. Table 14.2

demonstrates the loss of disinfection as pH increases:

Chlorine Disinfectants

The options for selecting the form of chlorine disinfectant

to use in pools are quite varied, and the choices are

complex. Table 14.3 gives the properties of each form.

Gas chlorine costs the least, and the relative cost of each

form of chlorine increases as you move right across the

table. The cost of the disinfectant tends to be less the

higher the concentration of available chlorine. The safety

issues are more complex than they might appear. The

hazards of gas chlorine are well known. The solid forms of

chlorine, such as calcium hypochlorite, are quite reactive.

When exposed to organic compounds, they can generate

a great deal of heat and are potentially explosive. Because

solid chlorine seems inert to the untrained worker, it is

often stored beside motor oil or gasoline or left in where

14-6 Residential Swimming Pools and Spas
Table 14.1. Pool Water Quality Problem Solving [7]

Healthy Housing Reference Manual 14-7
moisture can start a chemical reaction. Even a pencil with

a graphite core that drops from a shirt pocket into a

container of calcium hypochlorite could result in a

chemical reaction leading to a fire that would release free

chlorine gas [7].

The following chemical reactions produce chlorine byproducts that reduce the effectiveness of chlorine and

cause most eye irritation.

Cl2 + H2O = HCl + HOCl

Chlorine + Water = Hydrochloric Acid +

Hypochlorous Acid

HOCl + NH3 = H2O + NH2Cl

Hypochlorous Acid + Ammonia = Water +

Monochloramine

HOCl + NH2Cl = H2O + NHCl2

Hypochlorous Acid + Monochloramine = Water +

Dichloramine

HOCl + NHCl2 = H2O + NCl3

Hypochlorous Acid + Dichloramine = Water +

Nitrogen Trichloride

Tables 14.1–14.4 serve as a quick problem-solving

reference for the home pool owner and operator. The

CDC Web site (www.cdc.gov/healthyswimming) provides

a great deal of useful information for both the inspector

and the homeowner.

Pool Water Hardness and Alkalinity 

The ideal range of water hardness for a plaster pool is

200 to 275 ppm. The ideal range for a vinyl, painted, or

fiberglass surface is 175 to 225 ppm. Excess hardness causes

scaling, discoloration, and filter inefficiency. Less than

recommended hardness results in corrosion of most

contact surfaces.

Alkalinity should be 80 to 120 ppm. High alkaline levels cause

scale and high chlorine demand. Low levels cause unstable

pH. Sodium bicarbonate will raise the alkalinity level. The

pool water will be cloudy if alkalinity is over 200 ppm. 

Table 14.2. pH Effect on Chlorine Disinfection [7]

Table 14.3. Chlorine Use in Swimming Pools

14-8 Residential Swimming Pools and Spas
Table 14.4. Swimming Pool Operating Parameters [7]

Liquid Chemical Feeders

Positive Displacement Pump

A positive displacement pump is preferable to erosion

disinfectant feeders. Positive displacement pumps can be

set to administer varied and specific chemical dosage rates

to ensure that a pool does not become contaminated with

harmful microorganisms. A positive displacement pump

does need routine cleaning, descaling, and servicing.

Running a weak muratic acid or vinegar solution through

the pump weekly can minimize most major servicing of the

pump. Most service on the pump involves one of four areas:

1. the check valves are scaled, their springs are weak,

or valves are no longer flexible;

2. the diaphragm is cracked, leaking, or not flexible;

3. the drive cam needs replacement or requires

adjustment; or

4. the motor requires replacement.

Healthy Housing Reference Manual 14-9
Erosion and Flow-through Disinfectant Feeders

These feeders work by the action of water moving around

a solid cake of chlorine and eroding the cake. The feeders

work quite well for smaller pools, but require

considerable care and maintenance. The variables that

affect the effectiveness of erosion feeders are

1. solubility of the chlorine cake or tablet;

2. surface area of the cake or tablet;

3. amount of water flowing around the cake or

tablet;

4. concentration of chlorine in the cake or

tablet; and 

5. number of cakes or tablets in the feeder.

Note: For safety reasons, the disinfectant cake must not

be accessible.

Spas and Hot Tubs

Hot tubs (large tubs filled with hot water for one or more

people) or spas (a tub with aerating or swirling water) are

used for pleasure and are increasingly being

recommended for therapy. The complexity of these

devices increases with each new model manufactured.

Newer models often have both ozone and ultraviolet light

emitters for enhanced disinfection (see Disinfectants

section earlier in this chapter). However, the environment

of the spa and hot tub, if not cleaned and operated

correctly, can become a culture medium for

microorganisms. Because the warm water is at the ideal

temperature for growth of microorganisms, good

disinfection is critical. Table 14.5 provides suggested hot

tub and spa operating parameters. It is essential that all

equipment works properly and that the units are cleaned

and disinfected on a routine basis. Monitoring the water

temperature is very important and, depending on the

health of the user, can be a matter of life and death. Time

in the heated water should be limited, and the

temperature for pregnant users should be below 103°F

(39°C) to protect the unborn baby. 

References

1. Lee HL, Levy DA, Craun GF, Beach MJ,

Calderon RL. Surveillance for waterborne-disease

outbreaks—United States, 1999–2000. MMWR

2002; 51(SS08):1–28. Available from URL:

http://www.cdc.gov/mmwr/preview/mmwrhtml/

ss5108a1.htm.

2. US Environmental Protection Agency.

LT1ESWTR Disinfection profiling and

benchmarking: technical guidance manual.

Washington, DC: US Environmental Protection

Agency; 2003. Available from URL:

http://www.epa.gov/safewater/mdbp/pdf/

profile/lt1profiling.pdf.

3. Centers for Disease Control and Prevention.

Healthy swimming. Atlanta: US Department of

Health and Human Services; no date. Available

from URL:

http://www.cdc.gov/healthyswimming/. 

4. Centers for Disease Control and Prevention. Fecal

accidents response recommendations for aquatics

staff. Atlanta: US Department of Health and

Human Services; no date. Available from URL:

http://www.cdc.gov/healthyswimming/fecalacc.htm.

5. Broadbent C. Guidance on water quality for

heated spas. Rundle Mall, South Australia,

Australia: Public Environmental Health Service;

1996. Available from URL:

http://www.dh.sa.gov.au/pehs/publications/

monograph-heated-spas.pdf.

6. Michigan State University Pesticide Education

Program. Swimming pool pest management:

category 5A, a training guide for commercial

pesticide applicators and swimming pool

operators. Chapter 3: pool disinfectants and pH.

East Lansing, MI: Michigan State University; no

date. Available from URL:

http://www.pested.msu.edu/BullSlideNews/

bulletins/pdf/2621/E2621chap3.pdf.

7. National Swimming Pool Foundation. Certified

pool-spa operator handbook, 2004. Colorado

Springs, CO: National Swimming Pool

Foundation; 2004. Available from URL:

http://nspf.org.

Additional Sources of Information

American Academy of Pediatrics. Available from URL:

www.aap.org.

American National Standards Institute. Available from

URL: http://www.ansi.org.

American Red Cross. Available from URL:

www.redcross.org.

14-10 Residential Swimming Pools and Spas
American Trauma Society. Available from URL:

www.amtrauma.org.

Association of Pool and Spa Professionals. Available from

URL: http://www.nspi.org/.

Centers for Disease Control and Prevention, National

Center for Injury Prevention and Control. Available from

URL: www.cdc.gov/ncipc/factsheets/drown.htm. 

For more information about the CDC fecal accident

recommendations, go to URL:

http://www.cdc.gov/healthyswimming/

fecal_response.htm. 

For additional information about cryptosporidiosis,

go to URL: http://www.cdc.gov/healthyswimming/

cryptofacts.htm.

See also Web-based Injury Statistics Query and

Reporting System (WISQARS) [Online]. (2002).

National Center for Injury Prevention and Control,

Centers for Disease Control and Prevention. Available

from URL: www.cdc.gov/ncipc/wisqars. 

Children’s Safety Network. Available from URL:

http://www.childrenssafetynetwork.org.

Healthy Housing Reference Manual 14-11

Table 14.5. Spa and Hot Tub Operating Parameters [7]
Chlorine Institute, Inc. Available from URL:

http://www.cl2.com.

National Safe Kids Campaign. Available from URL:

http://www.safekids.org.

National Safety Council. Available from URL:

http://www.nsc.org/.

National Swimming Pool Foundation. Available from

URL: http://www.nspf.com/.

Think First National Injury Foundation. Available from

URL: http://www.thinkfirst.org.

US Consumer Product Safety Commission. Available

from URL: http://www.cpsc.gov.

14-12 Residential Swimming Pools and Spas