Self-supplied domestic withdrawal

estimated by census block for 2005

0

1−2,500

2,501−10,000

Greater than 10,001

(in gallons per day per square mile)

U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2009–1168

Prepared in cooperation with the 

New Hampshire Department of Environmental Services

Methods for Estimating Withdrawal and 

Return Flow by Census Block for 2005 and 2020 

for New Hampshire
Cover. Map shows the intensity of self-supplied domestic withdrawal estimated by census block for 2005 in New Hampshire.
Methods for Estimating Withdrawal and 

Return Flow by Census Block for 

2005 and 2020 for New Hampshire

By Laura Hayes and Marilee A. Horn

Prepared in cooperation with the 

New Hampshire Department of Environmental Services

Open-File Report 2009–1168

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2009

For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, 

natural hazards, and the environment, visit http://www.usgs.gov or call 1-888-ASK-USGS

For an overview of USGS information products, including maps, imagery, and publications, 

visit http://www.usgs.gov/pubprod

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Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Hayes, Laura, and Horn, M.A., 2009, Methods for estimating withdrawal and return flow by census block for 

2005 and 2020 for New Hampshire: U.S. Geological Survey Open-File Report 2009–1168, 32 p., available at 

http://pubs.usgs.gov/of/2009/1168.
iii

Acknowledgments

This project has been carried out with support from Sarah Pillsbury and Brandon Kernen of the 

New Hampshire Department of Environmental Services (NHDES). The authors would like to 

thank Johnna McKenna of NHDES for providing the Water Distribution and Sewer Collection 

Areas geographic information systems data, Linda Thompson of New Hampshire Drinking 

Water and Groundwater Bureau for providing a copy of the Drinking Water database, Frederick 

Chormann of the New Hampshire Geological Survey/NHDES for providing a copy of the state 

water-use registration database (WATUSE), and Daniel Dudley of NHDES for providing a copy of 

the National Pollutant Discharge Elimination System (NPDES) wastewater facility database. 

We would also like to thank Leslie DeSimone and Mark Nardi of the U.S. Geological Survey 

(USGS) for their critical reviews of the report. Appreciation also is extended to the following 

USGS employees: Kim Otto and Ruth Larkins for editorial reviews, Susan Bergin and Christine 

Mendelsohn for illustrations, and Ann Marie Squillacci for manuscript preparation and layout.

v

Contents

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Purpose and Scope ..............................................................................................................................1

Water-Use Concepts ............................................................................................................................2

Methods for Estimating Water Use.............................................................................................................2

Identifying Water Users.......................................................................................................................3

WATUSE Database ......................................................................................................................3

Drinking Water Database ...........................................................................................................5

NPDES Databases .......................................................................................................................5

Census Database.........................................................................................................................5

Population Estimates Database ................................................................................................5

The New Hampshire Water Demand Database .....................................................................5

Identifying the Source of Water and the Destination of Wastewater by Census Block.........11

Water Distribution and Sewer Collection Areas GIS Data Set ..........................................11

Census GIS Data Set .................................................................................................................11

GIS Processing...........................................................................................................................11

Growth Rate Calculations.........................................................................................................15

Manual Adjustments to GIS Script Output ............................................................................15

Quality Assurance......................................................................................................................18

Estimation of Water Use by Census Block .....................................................................................22

Assumptions ...............................................................................................................................22

2005 Registered Use..................................................................................................................22

2005 Unregistered Use..............................................................................................................22

Domestic Water Withdrawal and Return Flow............................................................23

Non-Domestic Water Withdrawal and Return Flow...................................................23

2020 Projections.........................................................................................................................23

Summary........................................................................................................................................................27

References Cited..........................................................................................................................................28

Glossary.........................................................................................................................................................29
vi

Figures

1. Flowchart showing relations among water-use activities ....................................................3

2. Flowchart showing approach and data sets used in estimating withdrawal and 

return flow by census block in New Hampshire .....................................................................4

3. Flowchart showing table structure of the New Hampshire Water Demand database ....6

4. Flowchart showing table structure linking the Drinking Water, National Pollutant 

Discharge Elimination System, and Water Use databases in the New Hampshire 

Water Demand database.............................................................................................................8

5. Diagram showing results of matching the Water Use, Drinking Water, and National 

Pollutant Discharge Elimination System databases in the New Hampshire Water 

Demand database, in number of facilities................................................................................9

6. Flowchart illustrating the logic followed to calculate the percentage of population in 

each census block served by water and (or) sewer ............................................................13

7. Map and table showing examples of calculated proportion of the population in 

each census block served by water and (or) sewer to estimate withdrawal and 

return flow....................................................................................................................................14

8. Flowchart representing the process used to add records to the AssociationWater 

table to represent census blocks with multiple community water systems.....................16

9. Flowchart representing the quality-assurance process used to adjust population 

that is self-supplied or served by any community water systems in the census block..19

10. Map showing example of a suite of community water systems and census blocks 

that are geographically interconnected .................................................................................20

11. Map showing the intensity of self-supplied domestic withdrawal estimated by 

census block for 2005 in New Hampshire ..............................................................................24

Tables

1. Derived data tables in the New Hampshire Water Demand database ...............................7

2. Example from the State Database Index table showing fields used to link facilities 

and their source and (or) destination identification numbers among the Water Use, 

Drinking Water, and National Pollutant Discharge Elimination System databases ........10

3. Percentages of census block population as assigned to 25-percent categories ...........12

4. Sample data from the AssociationWater table for a specific census block that is 

modified from the geographic information system script output to its final version 

by step ..........................................................................................................................................17

5. Quality-assured estimates of population served for a suite of interconnected 

community water systems and census blocks......................................................................21

6. Coefficients for estimation of industrial water demand from two-digit Standard 

Industrial Classification categories and number of employees .........................................25

7. Commercial facility water-demand estimates by water-use group...................................26
vii

Conversion Factors, Datum, and Acronyms

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

Area

acre 4,047 square meter (m2

)

acre 0.004047 square kilometer (km2

)

square mile (mi2) 2.590 square kilometer (km2) 

Volume

gallon (gal) 3.785 liter (L) 

gallon (gal) 0.003785 cubic meter (m3

) 

Flow rate

gallon per day (gal/d) 0.003785 cubic meter per day (m3

/d)

million gallons per day (Mgal/d) 0.04381 cubic meter per second (m3

/s)

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

ACRONYMS USED IN REPORT

CFCC Census Feature Class Code

CWS community water system

CWWS community wastewater system

FIPS Federal Information Processing Standards

GIS geographic information system

MCD minor civil division

NCWS non-community water system

NHDES New Hampshire Department of Environmental Services

NHDWGB New Hampshire Drinking Water and Groundwater Bureau

NHGS New Hampshire Geological Survey

NHOEP New Hampshire Office of Energy and Planning

NHWEB New Hampshire Wastewater Engineering Bureau

NPDES National Pollutant Discharge Elimination System

PWSID Public Water System identification number

SDWA Safe Drinking Water Act

SDWP Safe Drinking Water Program

SIC Standard Industrial Classification

STFID census block (Summary Tape File) identification number

TIGER Topologically Integrated Geographic Encoding and Referencing

USEPA United States Environmental Protection Agency

USGS United States Geological Survey

WATUSE water-use database maintained by the New Hampshire Geological Survey

WWTF wastewater-treatment facility

Abstract

The U.S. Geological Survey, in cooperation with the 

New Hampshire Department of Environmental Services, 

estimated the amount of water demand, consumptive use, 

withdrawal, and return flow for each U.S. Census block 

in New Hampshire for the years 2005 (current) and 2020. 

Estimates of domestic, commercial, industrial, irrigation, and 

other nondomestic water use were derived through the use and 

innovative integration of several State and Federal databases, 

and by use of previously developed techniques.

The New Hampshire Water Demand database was 

created as part of this study to store and integrate State of 

New Hampshire data central to the project. Within the New 

Hampshire Water Demand database, a lookup table was 

created to link the State databases and identify water users 

common to more than one database. The lookup table also 

allowed identification of withdrawal and return-flow locations 

of registered and unregistered commercial, industrial, 

agricultural, and other nondomestic users. Geographic 

information system data from the State were used in 

combination with U.S. Census Bureau spatial data to locate 

and quantify withdrawals and return flow for domestic users in 

each census block.

Analyzing and processing the most recently available 

data resulted in census-block estimations of 2005 water use. 

Applying population projections developed by the State to 

the data sets enabled projection of water use for the year 

2020. The results for each census block are stored in the 

New Hampshire Water Demand database and may be 

aggregated to larger political areas or watersheds to assess 

relative hydrologic stress on the basis of current and potential 

water availability.

Introduction

The New Hampshire Department of Environmental 

Services (NHDES) is developing a systematic, statewide 

assessment to quantify indicators of hydrologic stress at 

the level of individual stream segments and the areas that 

drain directly to these features. These local-scale data can be 

aggregated to larger areas and higher levels of organization 

within a hierarchy of watersheds to support regional 

assessments as needed.

The approach used by NHDES defines hydrologic stress 

as the ratio of cumulative net water withdrawal to estimated 

natural streamflow for each stream reach. Water withdrawal 

and return flow in New Hampshire must be quantified for 

assessing hydrologic stress. Registered water use (water 

withdrawn, used, or returned by facilities that use at least 

20,000 gal of water per day) is known because monthly 

pumpage is reported to the New Hampshire Geological Survey 

(NHGS) on a quarterly basis. The amount of water withdrawn 

and returned by those using less than 20,000 gal of water 

per day (unregistered users) is unknown and has not been 

estimated statewide. The U.S. Geological Survey (USGS) 

developed procedures for estimating unregistered water use 

as part of a detailed water-use analysis for the Seacoast region 

of New Hampshire (Horn and others, 2008). Estimates of all 

withdrawals and return flow can be made by combining the 

reported withdrawal and return-flow data for registered users 

with estimates of water use for unregistered users. NHDES 

also would like to assess potential water demand for 2020 and 

relate this demand to natural streamflows. To aid the waterresource planning efforts of NHDES, the USGS generated 

estimates of (1) current (2005) unregistered water withdrawal 

and return flow and (2) future (2020) total water withdrawal 

and return flow by census block throughout the State.

Purpose and Scope

This report details the methods used to estimate water 

withdrawal and return flow in 2005 and project water 

withdrawal and return flow for 2020 throughout the State 

of New Hampshire by U.S. Census block. The report also 

describes the New Hampshire Water Demand database, which 

was created during this study and contains versions of State 

databases that are linked through a new lookup table. Wateruse activities evaluated include water withdrawal, delivery, 

demand, consumptive use, release, return flow, and transfer 

(for an explanation of these water-use terms, see section 

entitled “Water-Use Concepts” and (or) the glossary). 

Methods for Estimating Withdrawal and Return Flow by 

Census Block for 2005 and 2020 for New Hampshire

By Laura Hayes and Marilee A. Horn
2 Methods for Estimating Withdrawal and Return Flow by Census Block for 2005 and 2020 for New Hampshire

Water-Use Concepts

In this report, water use generally refers to specific 

activities that involve the use of water by humans. Water-use 

activities begin when water is diverted or withdrawn from 

surface-water or groundwater sources and conveyed to a place 

of use (fig. 1). A withdrawal is made by an individual user 

or by a community water system (CWS) that may treat the 

water and convey (deliver) it to users through a distribution 

system (Horn, 2002). A CWS is defined as a public water 

system that delivers water for human consumption through 

pipes and other constructed conveyances and regularly serves 

at least 25 year-round residents or has at least 15 service 

connections used by year-round residents (U.S. Environmental 

Protection Agency, 1998). CWSs might serve towns, cities, 

military bases, apartment complexes, or mobile home parks. 

Users who obtain their water directly from a groundwater or 

surface-water source, and not from a CWS, are self-supplied. 

In this report, CWSs are divided into two groups: domestic 

CWSs that serve only domestic users in mobile-home parks, 

condominiums, and other residential developments, and 

multi-use CWSs that serve a mix of domestic, commercial, 

industrial, and irrigation users (Horn and others, 2008). 

A non-community water system (NCWS) is a different 

type of public water system that serves people either temporarily in residence (transient), as at a motel or restaurant, or 

regularly using the drinking-water supply without actually 

living at the site (nontransient), as at a business. For the purposes of estimating water demand in this report, the NCWSs 

are treated not as public water systems but as water users, 

because NCWSs use water at their location (unlike CWSs, 

which deliver water to other entities to use). Note that they are 

considered public water systems when discussing them in the 

context of the Safe Drinking Water Program (SDWP) and the 

Drinking Water database that supports the SDWP.

Water demand refers to water that is needed or used for a 

specific purpose by a single user or aggregate of users within 

a geographic area. Examples include domestic activities 

in a household (such as drinking or bathing), irrigation, or 

industrial processing. In this study, nine categories of water 

demand were estimated—domestic, commercial, industrial, 

golf-course irrigation, agricultural irrigation, hydroelectric, 

thermoelectric, mining, and aquaculture. Nondomestic water 

demand in this report refers to the eight categories of use other 

than domestic demand. 

Consumptive use refers to water that evaporates during 

use or is incorporated into a product and, therefore, is removed 

from the immediate environment. Unaccounted-for water use 

refers to water in a distribution system that leaks back into the 

hydrologic system, is used in firefighting, or is used for infrastructure maintenance (street cleaning, filter backwash at the 

treatment plant, or hydrant and system flushing) (Horn, 2002).

Wastewater can be returned by a user directly to the 

groundwater system through on-lot (septic) sewage disposal 

systems. It also can be returned to groundwater or surface 

water from the treatment facility of a community wastewater 

system (CWWS) after the users have released their wastewater to sewers and the wastewater has been conveyed to the 

treatment facility. Finally, wastewater can be returned from 

industrial and other nondomestic on-site wastewater-treatment 

systems to surface water or groundwater. All of these wastewater pathways are collectively called return flow (Horn and 

others, 2008). 

Water also can be transferred from one area into 

another—water leaving an area (political or drainage basin) 

is termed an export, and water entering an area is termed an 

import. Water moved from one watershed to another is called 

an interbasin transfer.

A state or any region may be divided into various 

geographic units for the purpose of grouping the users and 

estimating the amount of water use in each unit. In this report, 

three primary geographic divisions are considered: census 

blocks, minor civil divisions (MCDs), and watersheds. A 

census block is a geographic subdivision of a census block 

group and is the smallest geographic area for which the U.S. 

Census Bureau collects and tabulates population and housing 

counts (U.S. Census Bureau, 2007). The census block provides 

the most flexible basis for compiling water-use data, because 

it can be aggregated to many different watershed or political 

hierarchies and can be updated with information from more 

accurate and detailed studies as they become available. New 

Hampshire is made up of 34,728 census blocks; the average 

census block area is 0.27 mi2 or about 170 acres. In urban 

areas, a census block can be visualized as a rectangular plot 

of land surrounded by streets on four sides, about 4 acres in 

area. In rural areas where there is no street grid, census blocks 

are bounded by streets, streams, political boundaries, or even 

former railroad rights-of-way or power lines and can range 

in area up to several thousand acres. A MCD is a type of 

governmental unit that is the primary legal or administrative 

subdivision of a county (U.S. Census Bureau, 2007). In 

New Hampshire, MCDs are generally equivalent to towns 

except that some MCDs are unincorporated. A watershed 

is a geographic area that drains water to one outlet point. 

Watersheds can be subdivided into smaller drainage areas.

Methods for Estimating Water Use

Estimates of water use rely on understanding what factors 

influence water demand and its associated consumptive use, 

because changes in demand and consumptive use affect 

withdrawal and return flow. At the simplest level, the methods 

for estimating water demand can be grouped into three basic 

steps: (1) identifying the water users, (2) determining areas 

where withdrawal and return flow occur, and (3) estimating 

amounts of water demand and consumptive use to derive 

withdrawal and return flow.
Methods for Estimating Water Use 3

Identifying Water Users

Water users in New Hampshire were identified through 

compilation and analysis of water-use and related data 

from State and Federal databases. Three State programs 

in New Hampshire maintain databases used in identifying 

who withdraws and (or) returns water. These programs 

and databases include (1) NHGS’s water-use registration 

and reporting program and the State water-use database 

(WATUSE); (2) the New Hampshire Drinking Water and 

Groundwater Bureau (NHDWGB) and the Drinking Water 

database; and (3) the New Hampshire Wastewater Engineering 

Bureau (NHWEB) and the National Pollutant Discharge 

Elimination System (NPDES) databases. Population data 

and geographic-boundary files were obtained from the U.S. 

Census Bureau. Population estimates for 2005 and population 

projections for 2020 for MCDs were obtained from the New 

Hampshire Office of Energy and Planning (NHOEP) (fig. 2). 

All of the data collected for the study are stored and linked in 

the New Hampshire Water Demand database.

WATUSE Database

In 1987, New Hampshire State law established a wateruse registration and reporting programto gather data on the 

largest water users in the State (New Hampshire Geological 

Survey, 2007). This information is used by the State to assess 

water demand on the State’s aquifers, lakes, reservoirs, rivers, 

and streams. All facilities that use more than 20,000 gal/d 

averaged over any 7-day period or 600,000 gal in any 30-day 

period are required to register and report their monthly water 

withdrawal, delivery, release to sewers, and return flow by 

each source and destination. The program is now administered 

by the NHGS.. Data on the registrants and their reported 

water use are stored in the State WATUSE database. A copy 

of the WATUSE database with reported water use for 2005 

was obtained from NHDES (Frederick Chormann, written 

commun., 2006) in October 2006. 

Figure 1. Relations among water-use activities. [Conveyance is represented in the flowchart by arrows. (Modified from Horn, 

2002)].

Consumptive

Use 

User

Demand

Withdrawal Community Water

System Treatment

Unaccounted-For

Water

Inflow and

Infiltration 

Community Wastewater

System Treatment

Community Wastewater

System Collection

(Sewers) 

Community Water

System Distribution 

Return Flow

Transfer

Delivery

Release

Transfer

Industrial Wastewater

Treatment

Self-supply

Self-disposal (septic)

Transfer

Transfer

Transfer
4 Methods for Estimating Withdrawal and Return Flow by Census Block for 2005 and 2020 for New Hampshire

Figure 2. Approach and data sets used in estimating withdrawal and return flow by census block in New Hampshire.

2005 and 2020

Do

mestic water

demand and

consumptive use

by census block

2005 and 2020

Nondomestic

withdrawal

by user

2005 Non-com

munity

water system

data

Annual

per capita

model

results

2005 and 2020

Nondomestic

water demand and

consumptive use

2000

Population and

housing data

Source database

Analysis

2005 Community

water system

data

2005

Population

estimates

Water-us

e estimates

Reported withdrawal

and return flow

2000 to 2005

to 2020 MCD

gro

wth rates

2020 Projected

withdrawal

by user

2005 and 2020

Registered

withdrawal and

return flow by user

Water use group

com

mercial and

industrial

coefficients

2005 and 2020

Nondomestic

return flow

by user

2005 and 2020

Do

mestic

withdrawal by

census block

2005 and 2020

Unregistered

CWS withdrawal

by user

W

ATUSE Database

2005

Registered

water use

R

egistered users Domestic

us

ers

Unregister

ed

communit

y

water systems

Unregister

ed

nondomestic

us

ers

Gro

wth rates

State GIS Data

Water distribution area

and sewered area

2020

Population

projections

Census Database NPDES Database

2005

NPDES

data

Analysis

2005 and 2020

Do

mestic

return flow by

census block

[NPDES, National Pollutant Discharge Elimination System; WATUSE, water-use database maintained by the New Hampshire Geological Survey; MCD, minor civil division; GIS, geographic information system;

CWS, community water system]

Population Estimates Database Drinking Water Database
Methods for Estimating Water Use 5

Drinking Water Database

The NHDWGB has the responsibility to administer 

the Federal Safe Drinking Water Act (SDWA) and other 

statutes related to public drinking-water supplies. In order to 

support this program responsibility, the NHDWGB maintains 

a Drinking Water database of information on public water 

systems. The database contains information on population 

served, contact addresses, locations of sources, and details 

about status and types of systems and sources. A copy of 

the Drinking Water database was obtained from NHDWGB 

(Linda Thompson, written commun., 2007) in March 2007. 

NPDES Databases

The NHWEB has the responsibility of working with the 

U.S. Environmental Protection Agency (USEPA) in support of 

the NPDES permit program under the Clean Water Act. The 

responsibility of the NHWEB is to ensure that the operation 

and maintenance of wastewater-treatment facilities (WWTFs) 

are in accordance with the Federal NPDES discharge permits 

for each facility by providing compliance inspections, technical assistance, operator training, and operator certification 

(New Hampshire Department of Environmental Services, 

2006). Furthermore, the NHWEB certifies discharge permits 

under the Federal NPDES permit program to ensure that the 

wastewater discharges do not violate applicable State rules and 

regulations. In order to support this program responsibility, the 

NHWEB maintains the NPDES databases. These databases 

include information on wastewater facilities, such as contact 

addresses, locations of discharge pipes, and details about 

status and types of systems. Copies of the NPDES databases 

were obtained from NHDES (Daniel Dudley, written commun., 2007) in December 2007. 

Census Database

Data were obtained from the U.S. Census Bureau in both 

tabular and spatial formats (U.S. Census Bureau, 2001, 2006). 

The population and housing-unit data from tabular census 

files, collectively known as Summary File 1, were joined to 

the spatial representation of census blocks. The census data 

sets are the most accurate, best documented demographic and 

housing data available and are associated with geographic 

regions at multiple scales. 

Population Estimates Database

The NHOEP develops and maintains databases of population estimates for years between the official decennial counts 

by the U.S. Census Bureau and of projections for future years 

(New Hampshire Office of Energy and Planning, 2007a, 

2007b). Population estimates for the year 2005 and population projections for the year 2020 were obtained from these 

databases for each MCD.

The New Hampshire Water Demand Database

The New Hampshire (NH) Water Demand database 

was developed in Microsoft Access as a tool to integrate and 

analyze water-use data. An overview of the structure of the 

NH Water Demand database, including the relations among 

individual tables, is shown in figure 3. The database includes 

tables from the three State water-use databases, the Census 

database, and the Population Estimates database, plus links to 

the State geographic information system (GIS) data on CWS 

distribution and CWWS collection systems (yellow boxes 

in fig. 3). Tables that were created during the processing and 

manipulating of the source data, including data from GIS 

analyses, are also part of the NH Water Demand database and 

are represented by blue boxes in figure 3. These tables are 

named and described in table 1. Queries were developed to 

create the final results (green boxes in fig. 3).

The three State databases (WATUSE, Drinking Water, 

and NPDES) were linked together to ensure that withdrawal 

and return flow by individual users were not double counted 

(and that if a reported value was available, an estimated value 

was not required). Facilities that were common to any two of 

the three databases were identified, and a lookup table called 

the State Databases Index (fig. 4) was established. The number 

of facilities in New Hampshire common to multiple databases 

is shown in figure 5. Table 2 shows an example of information 

for a facility in all three databases. In addition to identifying 

unique facilities, linking the State databases also ensured that 

each point of withdrawal and return is unique in the NH Water 

Demand database. 

In table 2, the unique identification numbers for facilities 

and source/destination points are provided as examples. 

In WATUSE, each registered facility has a unique 5-digit 

number (WU_ID), beginning with a “2.” Each source in 

WATUSE has a unique identification number (Source_ID) 

containing the WU_ID, followed by a dash, the letter “S,” 

and a 2-digit number, such as “01.” Each destination has a 

unique identification number (Destination_ID) containing 

the WU_ID, followed by a dash, the letter “D,” and a 2-digit 

number, such as “01.” In the Drinking Water database, each 

public water system has a unique 7-digit identification number 

(PWSID). Each source in the Drinking Water database has a 

unique identification number (Source_Entity_ID) containing 

the PWSID, followed by a dash and a 7-digit number, such 

as “0000002.” In the NPDES database, each facility has 

a unique identification number (NPDES_ID), which has 

nine alpha-numeric characters beginning with “NH.” Each 

destination (discharge point) in the NPDES database has a 

unique identification number (Discharge_Entity_ID) in one of 

a variety of formats. 

In addition to identifying common facilities, it was 

necessary to create a link in the State Databases Index table 

between points of withdrawal in each database and points 

of return flow in each database to ensure that reported data 

were properly included in the final water-use estimates. Water 

sources and discharge points common to more than one State 
6 Methods for Estimating Withdrawal and Return Flow by Census Block for 2005 and 2020 for New Hampshire

Figure 3. Table structure of the New Hampshire Water Demand database.

2005 and 2020

Unregistered

(nondomestic)

withdrawal by user

2005 and 2020

Domestic

return flow by

census block

Source database tabl

es Deriv

ed data tabl

es

[USEPA, United States Environmental Protection Agency; PWSID, Public Water System identification number; GIS, geographic information system; STFID, census block identification

number; WU, water use; (Derived data tables are described in table 1.)]

Water-us

e estimates

RegRep2005

Town

Growth Rate

2005 and 2020

Registered

withdrawal and

return flow by user

WaterUseGroup

NHDemand

2005 and 2020

Unregistered

(nondomestic)

return flow by user

2005 and 2020

Domestic

withdrawal by

census block

ReportedWaterUse2005

WU_FlagCodes

WATUSE Database Distribution area

State GIS Database

and sewered area

2000

Population and

housing data

Census Database

2005

Population

estimates

2020

Population

projections

Permits Active

Discharge Entities

DecLatDecLonNPDES

NPDES Database

Association

Water

Association

Sewer

2005 Community 2005 Non-community

Water System Inventory

Source and Entity

Latitude and Longitude 2003

System Category Codes

EPA System Type Code

Dri

Old PWSID to New PWSID

nking Water Database

SystemWU

State

Databases

Index

Seacoast

PerCapita

PerPWSID

RegAllWuid

Population Estimates

TownSTFID

Database
Methods for Estimating Water Use 

7

Table 1. Derived data tables in the New Hampshire Water Demand database.[WATUSE, water-use database maintained by the New Hampshire Geological Survey; NPDES, National Pollutant Discharge Elimination System; STFID, census block identification number; SIC, Standard Industrial Classification; PWSID, Public Water System identification number; GIS, geographic information system; CWS, community water system; CWWS, community wastewater system; WU_ID, Unique number assigned to the water user in the WATUSE database; NPDES_ID, National Pollutant Discharge Elimination System identification number]

Table name Origin Description Data content

State Databases Index Drinking Water Database; WATUSE 

Database; and NPDES Database

Links the 3 State databases by providing for each user 

and their well, intake, or discharge pipe the permit number and unique record-identification number used in each State database

Name, permit numbers, STFID, town, county, 

latitude and longitude for each well, intake, and discharge pipe.

WaterUseGroupNHDemand Seacoast Water-Use Database 

(Horn and others, 2008)

Water demand per employee by industrial SIC code; 

water demand by facility by type of commercial business

Description of business and estimated water 

demand.

SeacoastPerCapitaPerPWSID Seacoast Water-Use Database 

(Horn and others, 2008)

Domestic per capita water demand by community 

water system as determined by the regression model in the seacoast area

PWSID and per capita value.

SystemWU Drinking Water Database; WATUSE 

Database; NPDES Database; and other derived tables

2005 and 2020 estimated or reported demand by user User permit numbers, name, description, population served, water-use code, facility or employee 

relationship, 2005 and 2020 demand estimate or reported value, STFID.

RegAllWuid WATUSE Database Reported withdrawal and return flow for registered 

users in 2005; estimated withdrawal and return flow for same users for 2020

User and source/discharge permit numbers, name, 

SIC code, facility or employee relationship, reported 2005 value and estimated 2020 value, latitude and longitude, STFID.

AssociationWater State GIS data and Drinking Water 

Database

Relationship between STFID and CWS; used in 

determining population served in each census block

STFID, PWSID, WU_ID, 2000, 2005, and 2020 

original population and 2000, 2005, and 2020 adjusted population served.

AssociationSewer State GIS data and NPDES Database Relationship between STFID and CWWS; used in 

determining population served by sewers in each census block

STFID, NPDES_ID, WU_ID, 2000, 2005, and 2020 

original population and 2000, 2005, and 2020 adjusted population served.

Town Growth Rate Census data (U.S. Census Bureau, 

2001) and Population Estimates Database (NHOEP, 2007a and 2007b)

Town growth rates developed from the 2000 Census 

town population, the 2005 population estimates by town, and the 2020 population projections by town

Town name, growth rate from 2000 to 2005, and 

growth rate from 2000 to 2020.

TownSTFID Census Database (U.S. Census Bureau, 

2006) and GIS data sets

Relationship between STFID and town; used in 

applying town growth rate to census blocks

STFID and town name.
8 Methods for Estimating Withdrawal and Return Flow by Census Block for 2005 and 2020 for New Hampshire

Figure 4. Table structure linking the Drinking Water, National Pollutant Discharge Elimination System, and Water Use databases in the New Hampshire Water Demand database.

System

Category

Codes

Source and

Entity 

Water

System

Inventory 

State Databases Index

State database table

PWSID Latitude and

Longitude

2003

NPDES

Discharge

Entities

NPDES

Permits

Active 

NPDES_ID

NPDES_ID and

Discharge_Entity_ID

WATUSE

Permits

PWSID PWSID and Source_Entity_ID

NPDES_ID

WU_ID

WU_ID andSource_ID or Destination_ID 

Lookup table

2005

Reported

NPDES

Discharge 

2005

Reported

Withdrawal

Discharge 

WATUSE

Source or

Destination

WU_ID

State database

Drinking Water database

WATUSE database NPDES database

[WATUSE, water-use database maintained by the New Hampshire Geological Survey; WU_ID, Unique number assigned to the water user in the WATUSE database; Source_ID, water source identification number in theWATUSE database; Destination_ID, wastewater destination identification number in the WATUSE database; PWSID, Public Water System identification number; Source_Entity_ID, water source identification number inthe Drinking Water database; NPDES, National Pollutant Discharge Elimination System; NPDES_ID, National Pollutant Discharge Elimination System identification number; Discharge_Entity_ID, discharge pointidentification number in NPDES database] 
Methods for Estimating Water Use 9

database were identified using the latitudes and longitudes and 

descriptive names in the databases. This was complicated by 

the facts that the databases were not equally up-to-date and 

did not store the data in a parallel manner. The Drinking Water 

and NPDES databases contain unique withdrawal or return 

locations when more than one location exists for a facility. 

The WATUSE database provides only one discharge location 

per facility and, for some facilities, combines many wells and 

surface-water intakes into one source location. Therefore, 

the discharge points could not be matched and the number of 

sources matched was low. The total discharge amounts and 

locations from the WATUSE database were incorporated into 

the NH Water Demand database. When a one-to-one match 

was not made between sources in WATUSE and the Drinking 

Water database, the reported withdrawal obtained from 

WATUSE was apportioned manually among all sources listed 

as active in the Drinking Water database table. 

Reported withdrawal and return flow values from the 

WATUSE database were used in estimating withdrawal and 

return flow for facilities not required to report to the state; 

the methods for estimating these flows are described in the 

“Estimating Water Use by Census Block” section of this 

report. A small number of publicly supplied, non-domestic 

users that use less than 20,000 gal/d are not in WATUSE 

or the Drinking Water database. The return flow from this 

small number of users is not estimated. However, return flow 

from domestic users that are on public water supply but not 

on sewers is estimated using the methods described in the 

“Identifying Source of Water and Destination of Wastewater 

by Census Block” section.

Data from the Census database were integrated with the 

water-use data using the census block identification system. 

In the Census database, each census block is associated 

with a 15-digit unique identifier (STFID) composed of four 

geographic codes. For example, the STFID 330019501001000 

is a concatenation of the State Federal Information Processing 

Standards (FIPS) code 33, the county FIPS code 001, the 

census tract code 950100, and the census block number 1000. 

The STFID is included in all tables that reference withdrawal 

and return-flow points for all nondomestic users, CWSs, and 

CWWSs in the NH Water Demand database.

Figure 5. Results of matching the Water Use, Drinking Water, and National Pollutant Discharge 

Elimination System databases in the New Hampshire Water Demand database, in number of 

facilities.

WATUSE

454

Drinking Water

2,198

NPDES

23

0

14

173

235

[WATUSE, Water-use database maintained by the New Hampshire Geological Survey;

NPDES, National Pollutant Discharge Elimination System database]
10 Methods for Estimating Withdrawal and Return Flow by Census Block for 2005 and 2020 for New Hampshire Table 2. Example from the State Database Index table showing fields used to link facilities and their source and (or) destination identification numbers among the Water Use, Drinking Water, and National Pollutant Discharge Elimination System databases. [WATUSE, water-use database maintained by the New Hampshire Geological Survey; WU_ID, Unique number assigned to the water user in the WATUSE database; Source_ID, water source identification number in the WATUSE database; Destination_ID, wastewater destination identification number in the WATUSE database; PWSID, Public Water System identification number; Source_Entity_ID, water source identification number in the Drinking Water database; NPDES, National Pollutant Discharge Elimination System; NPDES_ID, National Pollutant Discharge Elimination System identification number; Discharge_Entity_ID, discharge point identification number in NPDES database] Permit holder Resource Action WATUSE database Drinking Water database NPDES database WU_ID Source_ID Destination_ID PWSID Source_Entity_ID NPDES_ID Discharge_Entity_ID Greenville Water Department Reservoir 1 Withdrawal 20047 20047-S01 0991010 0991010-0000002 NHG640009 Greenville Water Department Reservoir 1 Return flow of filter backwash 20047 20047-D01 0991010 NHG640009 640009-001
Methods for Estimating Water Use 11

Identifying the Source of Water and the 

Destination of Wastewater by Census Block

In order to estimate water withdrawal and return flow 

for each census block, the source of water and destination of 

wastewater for users in each census block had to be assigned. 

The latitude and longitude of each NCWS and CWS point of 

withdrawal were obtained from the Drinking Water database 

and associated with the appropriate census block. Similarly, 

the latitude and longitude of each CWWS point of return 

flow were obtained from the NPDES database and associated 

with the appropriate census block. To locate and quantify 

withdrawal and return flow for domestic users, the numbers 

of domestic users on self-supply, public supply, self-disposal 

(on-site disposal), and public disposal were estimated for 

each census block, so that the self-supply/self-disposal 

portions could be attributed to the census block in which the 

user resides. This was accomplished through the use of two 

GIS data sets: the NHDES Water Distribution and Sewer 

Collection Areas data set (Johnna McKenna, NHDES, written 

commun., 2003) and U.S. Census Bureau block data set 

(U.S. Census Bureau, 2006). 

Water Distribution and Sewer Collection Areas 

GIS Data Set

NHDES created the polygon areas in the Water 

Distribution and Sewer Collection Areas data set by buffering 

the community water-distribution lines and sewer lines by 

200 ft on each side. The data set was originally based on 

NH Department of Transportation (DOT) road locations, 

and the version used for this study was last revised in 2003. 

Areas of overlap between community water and wastewater 

systems are stored in the data set as single features with the 

attribute “pipe_type” set to “both.” The PWSID for a CWS 

is associated with each contiguous water-distribution area 

that is part of the same system. The PWSIDs were used to 

link the Drinking Water database to this GIS data set. Links 

between this GIS data set and the NPDES database were 

established through the AssociationSewer table, described in 

the “Manual Adjustments to GIS Script Output” section of this 

report. Areas outside of the buffered lines were assumed to be 

self-supplied.

The Water Distribution and Sewer Collection Areas data 

set has limited accuracy for the following reasons:

• The water distribution and sewer collection lines 

have been buffered to depict areas and, therefore, 

capture some parts of other roads within 200 ft that 

are not served;

• The data set shows the entire system, including conveyances that extend from the source of supply to the 

distribution system and may cross roads that are not 

actually served by the system;

• Water distribution or sewer collection lines may have 

been extended since the last revision of the data set; 

and

• The buffered lines were based on the NH DOT road 

data set rather than the census road data set, which 

may result in some minor discrepancies with the 

census blocks.

Census GIS Data Set

The U.S. Census Bureau has been working to improve 

the accuracy of the digital line data that represent the 

roads, rivers, railroads, and other geographic features in 

their Topologically Integrated Geographic Encoding and 

Referencing (TIGER) database (U.S. Census Bureau, 2006). 

The Census Bureau relies on various Federal, state, local, and 

commercial data, including NH DOT data, to accomplish this 

goal. In December of 2006, the first available release of an 

updated digital line data set for New Hampshire was obtained, 

including the census block boundaries and the roads packaged 

by county (U.S. Census Bureau, 2006). The county data were 

converted from TIGER files to ArcGIS-compatible files and 

merged to create a statewide data set. 

Together, the U.S. Census Bureau and the Water 

Distribution and Sewer Collection Areas data sets provided 

the means to estimate water withdrawal and return flow. The 

census population counts are associated with geographic areas 

(census blocks) that share geometry with the roads, and the 

water-distribution and wastewater-collection systems generally 

follow the roads. Therefore, overlays of the roads and waterdistribution and wastewater-collection areas can be used to 

derive estimates of the number of domestic users per census 

block publicly supplied or self-supplied and the number that 

are on sewers or septic systems. 

GIS Processing

In order to estimate domestic water withdrawal and return 

flow, estimates of the population served by CWS or CWWS 

in each census block were needed. The following assumptions 

were made to generate these estimates:

• Houses are not built along divided highways. 

• Populations are evenly distributed along all other roads.

• The proportion of a census block’s perimeter roads 

with water distribution lines is also the proportion of 

that census block’s population served by water (and 

similar proportionality exists for sewer lines). 

Therefore, calculating the length of each road segment 

that coincides with the water-distribution and wastewatercollection areas provides estimates of populations served by 

water and (or) sewer systems. From these lengths of road 

segments, proportions for each census block’s perimeter 
12 Methods for Estimating Withdrawal and Return Flow by Census Block for 2005 and 2020 for New Hampshire

(excepting highways) were calculated. Manual reviews 

of these calculations for quality-assurance purposes 

were conducted. 

A preliminary GIS processing step identified all roads 

that form census-block boundaries and are associated with 

housing in order to use this subset of roads in subsequent GIS 

processing. All the TIGER linework is packaged in one file 

with each feature type (for example, road, railroad, physical 

feature, hydrography) noted in an attribute called “CFCC,” 

or Census Feature Class Code (U.S. Census Bureau, 2007). 

Road features (CFCC starting with “A”) were selected and 

saved to a separate file. Each line representing a road has a 

left and right side, defined by the direction of the line as it 

was originally drawn. As such, attributes stored in the road 

table include the state, county, tract, and 4-digit census block 

identification numbers of the polygons on each side of the 

road. In order to tie the road features to the 15-digit STFID in 

the tabular census data, the four attributes on the left side were 

concatenated to form a field called STFID_L, and four fields 

were concatenated to create STFID_R for the right side.

Any road segment with STFID_L not equal to STFID_R 

represents a road on the boundary between two census blocks. 

Road segments with CFCC starting with A1 are “Primary 

Highways with Limited Access.” Roads on the outer perimeter 

of a census block that are not highways were selected and 

saved into a GIS data set of modified roads.

Road classes defined by the U.S. Census Bureau as 

one-lane dirt trails or roads typically inaccessible to motor 

vehicles also were examined in order to determine whether to 

exclude them from the analysis of population served. If few 

or no houses existed on these dirt roads, including them could 

invalidate the assumption that the population of each census 

block is evenly distributed on its roads. The analysis was run 

with and without these classes of dirt roads, and no difference 

in percent population served was observed. 

A GIS script (program) was written that looped through 

each unique census block in New Hampshire and determined 

the proportion of people served by CWSs and CWWSs 

(fig. 6). During each iteration, first, the STFID, population, 

and housing-unit values of one census block were extracted 

and stored in variables for use in a subsequent analysis. 

Next, all census block boundary roads in the modified data 

set that surround that particular census block were selected 

(STFID_L or STFID_R equal to the STFID of the census 

block) and saved to a temporary file used for only one 

iteration. These roads were geometrically intersected with the 

Water Distribution and Sewer Collection Areas data set to add 

pipe type (water, sewer, both, or none), length, and PWSID 

attributes to the roads table. The lengths of all the roads in the 

temporary file were summed, and the lengths of each pipe type 

were summed. 

A temporary table was created to store data gathered and 

calculated for each census block, including STFID (“STFID”), 

population (“pop00”), housing units (“hu00”), total length 

of roads (“rds_total”), length of roads with water only 

(“rds_water”), length of roads with sewer only (“rds_sewer”), 

length of roads with water and sewer (“rds_both”), and 

the minimum and maximum PWSIDs (“minpwsid” and 

“maxpwsid”). To estimate the proportion of the population in 

that census block served by water, the proportion of length of 

water lines to total length of roads was calculated (“pct_water” 

= (rds_water + rds_both) / rds_total). Similarly, the length 

of sewer lines to the total length of roads also was calculated 

(“pct_sewer” = (rds_sewer + rds_both) / rds_total). During 

each iteration of the script, the row from this temporary table 

was added as a record to a comma-delimited text file resulting 

in a table with one row per census block (fig. 7). 

If the roads in a census block were served by only one 

system or no systems, the minimum and maximum PWSIDs 

were the same. A record with minimum and maximum 

PWSIDs that differed indicated a census block that was served 

by more than one system; further analysis would be needed 

to determine how many systems serve that block and how to 

apportion the block’s population among the systems. 

A sample from the Water Distribution and Sewer 

Collection Areas data set and a table of calculated proportions 

for five example census blocks (highlighted with a yellow 

inner border) are shown on figure 7. Roads shown in black 

were included in the census block boundary data set; roads 

shown in gray were not. There is only one CWS in the town 

shown in figure 7, so “minpwsid” equals “maxpwsid” in all 

five example census blocks. In census block example number 

2, the census block is bounded on the southwest side by a 

highway, which was eliminated from the analysis by the 

previously discussed assumptions. Consequently, the entire 

population of that census block was assumed to live along 

the other roads that compose the boundary, which is why the 

proportion served by water is close to 1.00 (or 100 percent) 

even though one side of the block has no CWS. Because 

of the inherent inaccuracies in the combination of multiple 

data sources, it was considered unreasonable to quantify the 

proportion of the population served by water or sewer more 

precisely than to the nearest 25 percent; the estimates were 

assigned to categories as shown in table 3. 

Table 3. Percentages of census block population as assigned 

to 25-percent categories.

[CWS, community water system; CWWS, community wastewater system]

Percentage of census block’s population 

with CWS (or CWWS) Assigned category

0–10 0

11–36 0.25

37–63 0.50

64–89 0.75

90–100 1.00
Methods for Estimating Water Use 13

Figure 6. Flowchart illustrating the logic followed to calculate the percentage of population in each census block 

served by water and (or) sewer.

Select block in row a

Store STFID, population, and

 housing units as variables:

stfid, pop00, hu00

Select roads surrounding

that block (roads with STFID_L =

stfid or STFID_R = stfid)

Are any

roads selected?

NO YES

Set variables:

minpwsid = 0

maxpwsid = 0

rds_tot = 0

rds_wat = 0

rds_both = 0

rds_sew = 0

Save selected roads

 to temp_rds coverage

Intersect temp_rds with water

and sewer buffer areas to create

rds_served (adds attributes 

pipe_type, length, and pwsid)

Sum the lengths of all

segments in rds_served and

store in variable rds_tot

Select roads with pipe_type = Water;

sum their lengths;

and store in variable rds_wat

For roads with pipe_type = Water 

or pipe_type = Both,

store minimum and maximum

pwsids in variables

minpwsid and maxpwsid

Create a temporary table

and populate one row

 with all stored variables

Calculate the percentage of roads

served by water and the percentage

of roads served by sewer

Add this table’s row to a

comma-delimited text file

Delete temporary files

and clear variables

Return to beginning

for loop a = a + 1

Begin loop a

Select roads with pipe_type = Both;

sum their lengths;

and store in variable rds_both

Select roads with pipe_type = Sewer;

sum their lengths;

and store in variable rds_sew

[STFID, census block identification number; STFID_L, identification number of the census block on the left; STFID_R, identification number of the census 

block on the right; pop00, 2000 population count; hu00, 2000 housing unit count; pipe_type, attribute indicating whether that segment of road is served by

water distribution, sewer collection, both, or neither; minpwsid, Minimum system identification number; maxpwsid, Maximum system identification number;

rds_tot, Total length of roads; rds_wat, Length of roads inside "water" areas; rds_both, Length of roads inside "both" areas; rds_sewer, Length of roads

inside "sewer" areas]
14 Methods for Estimating Withdrawal and Return Flow by Census Block for 2005 and 2020 for New Hampshire

Figure 7. Examples of calculated proportion of the population in each census block served by water and (or) sewer to estimate withdrawal and return flow.

Interstate 89

oC t n

oo

oc ko

i R ev r

1

2

3

4

5

12345

STFI

D pop00 hu00 minpwsid maxpwsid rds_total rds_water rds_both rds_se

wer pct_water pct_sewer

330130390002010 32 12 1191010 1191010 3556.63 1754.66 1560.19 0 0.93 0.44

330130390002017 104 43 1191010 1191010 8220.4 4761.71 3100.82 0 0.96 0.38

330130390002027 15 9 0 0 1638.83 0 0 0 0 0

330130390004005 68 26 1191010 1191010 5557.19 3353.75 2203.45 0 1.00 0.40

330130390004009 29 11 1191010 1191010 1683.3 0 1683.30 0 1.00 1.00

71°44' 71°43'30” 71°43' 71°42'30" 71°42'

43°13'30"

43°14'

0 500 1,000 FEET0 125 250 METERS

43°13'

Water Distribution and Sewer Collection Areas from New Hampshire Department of Environmental Services, 2003;Roads, hydrography and block boundaries from U.S. Census Bureau, 2006;New Hampshire State Plane Coordinate System, North American Datum 1983

[Census blocks are bounded by black or gray roads or blue streams; CWS, community water system; CWWS, community wastewater system. Field definitions for table: STFID, Unique census block 

number; pop00, 2000 population count; hu00, 2000 housing unit count; minpwsid, Minimum system identification number; maxpwsid, Maximum system identification number; rds_total, Total length of roads from block boundary dataset; rds_water, Length of roads inside ‘water’ areas; rds_both, Length of roads inside ‘both’ areas; rds_sewer, Length of roads inside ‘sewer’ areas; pct_water = (rds_water + rds_both) / rds_total; pct_sewer = (rds_sewer + rds_both) / rds_total]

EXPLANATION

Water distribution andsewer collection areas

Pipe type

Water (CWS)Sewer (CWWS)BothCensus hydrographyRoads in block boundary dataset

Census roads

Inner border of blocksselected as examples

Block interior roads orprimary highways (notincluded in calculations)
Methods for Estimating Water Use 15

Growth Rate Calculations

For each MCD, the 2000 census population by town, 

population estimates from NHOEP for the year 2005, and 

population projections from NHOEP for the year 2020 were 

used to calculate growth rates from 2000 to 2005, from 2000 

to 2020, and from 2005 to 2020 (New Hampshire Office of 

Energy and Planning, 2007a, 2007b). Reports by the NHOEP 

do not include unincorporated places, so the 25 unincorporated 

MCDs were assumed to have no increase or decrease in population and were assigned growth rates equal to 1.0.

In order to estimate domestic water demand, the estimated 2005 population in each census block was calculated 

as the 2000 census block population multiplied by the MCD 

growth rate between 2000 and 2005. Similarly, the projected 

2020 population in each census block was calculated as the 

2000 census block population multiplied by the MCD growth 

rate between 2000 and 2020. To estimate the 2020 water 

demand for registered users with reported 2005 values and 

unregistered, non-domestic users with 2005 estimates, the 

population growth rate from 2005 to 2020 was calculated and 

applied to those existing 2005 values. 

Manual Adjustments to GIS Script Output

The table resulting from the automated GIS process 

contains records of estimated proportions of populations 

served by CWSs or CWWSs and the 2000 population. 

Additional records were needed to store the categories of 

estimated percentages for self-supplied users and users with 

on-site disposal, as well as the adjustments in population 

served when there is more than one CWS in the census block. 

Separate tables (AssociationWater and AssociationSewer) 

were created to analyze the source of supply and destination of 

wastewater. The steps in this process for the source of supply 

are shown in figure 8. (A similar process was used for the 

destination of wastewater). In the AssociationWater table, the 

fields minpwsid and maxpwsid correspond to the PWSID(s) 

serving the census block, and in the AssociationSewer table, 

these fields were changed to correspond to the NPDES_ID(s). 

These “association” tables were manually revised to 

ensure that each census block had separate records to show 

self-supplied populations and each CWS that serves the census 

block. All the steps used to modify the output from the GIS 

script to the final version of the AssociationWater table are 

shown using the examples in table 4. An example row from 

the table resulting from the GIS script is shown at the top 

of table 4. Step 1 (shown in yellow in table 4 and figure 8) 

represents the initial creation of the AssociationWater table, 

which was accomplished by pulling some of the fields from 

the GIS output file. 

Step 2 (shown in green in table 4 and figure 8) shows the 

fields Assoc_ID (unique record number), cat_pct (category 

percent with values of 0, 0.25, 0.50, 0.75, and 1.00), pop05 

(estimated 2005 population), and pop2020 (projected 2020 

population) that were added to the AssociationWater table. 

The Assoc_ID field is a unique record number automatically 

assigned as the record was added. The proportion of the 

population in that census block served by water, as calculated 

by the GIS script, was converted to a category percentage, 

according to table 3. Population estimates for 2005 and 

population projections for 2020 by census block were obtained 

from a table containing results of the growth rate calculations.

Step 3 (shown in blue in table 4 and figure 8) shows that 

a record was added for the self-supplied portion of a census 

block with at least one CWS, and another record was added if 

there was a second CWS. An initial value of zero in minpwsid 

indicated the entire census block was self-supplied, and the 

percent category was 1.00. When the value in minpwsid field 

was not zero, the value in cat_pct represented the portion of 

the population in that census block served by any CWS. A 

second record for that census block was added to the table to 

represent the self-supplied portion of the population, and its 

minpwsid was assigned 0. Because the publicly supplied and 

self-supplied portions must sum to 100 percent, the percent 

category in the new record was 1.00 minus the value in the 

first record. For example, if the percent category (cat_pct) 

was 0.25, then 0.75 was assigned to the self-supplied portion 

of the census block. In a census block with more than one 

CWS, the minpwsid was not equal to the maxpwsid in the 

AssociationWater table, so a third record was added to the 

AssociationWater table to represent the population served by 

the maxpwsid. The value in maxpwsid was assigned to the 

minpwsid field for that record. No population served value 

was associated with the second CWS at the time. Rarely, more 

than two CWSs serve the same census block. The approach 

used to identify other CWSs and to divide the population 

served among all the CWSs is described in the “Quality 

Assurance” section.

Step 4 (shown in orange in table 4 and figure 8) 

focused on calculating the population served by a CWS by 

multiplying the category percent by the 2000, 2005, and 2020 

populations. First, however, the fieldname minpwsid was 

changed to PWSID and the field maxpwsid was removed 

from the AssociationWater table as it was no longer needed. 

(In the case of the AssociationSewer table, minpwsid was 

changed to NPDES_ID.) Then, the automatically adjusted 

self-supplied and CWS-supplied populations for 2000 were 

calculated by multiplying the percent category (0.00, 0.25, 

0.50, 0.75, or 1.00) by the original 2000 population. The 

population values were rounded to the nearest whole number. 

The ratio of self-supplied users to publicly supplied users was 

assumed to remain the same for 2005 and 2020, so the same 

percent category was multiplied by the original 2005 and 2020 

populations to create the automatically adjusted self-supplied 

and CWS-served populations for 2005 and 2020. Step 5 is 

described in the following section “Quality Assurance.”
16 Methods for Estimating Withdrawal and Return Flow by Census Block for 2005 and 2020 for New Hampshire Figure 8. Flowchart representing the process used to add records to the AssociationWater table to represent census blocks with multiple community water 

systems.

Do not add a new record

Does the census

block have a “0” value

for minpwsid? 

No Yes

Create a new record with

minpwsid equal to “0”

Select block in a row

Create

AssociationWater

table with a

record for every

census block 

[GIS, geographic information system; Field definitions for table: Assoc_ID, unique record number for the AssociationWater table; cat_pct, category percent; pop05, estimated 2005 population; pop2020, projected 2020

population; minpwsid, minimum system identification number; maxpwsid, maximum system identification number; PWSID, Public Water System identification number; colored boxes relate the steps to those in table 4]

For minpwsid = 0,

cat_pct = 1.00 minus

cat_pct for minpwsid ≠ 0

Does

minpwsid = maxpwsid? 

Create a new record with

minpwsid equal to maxpwsid

No Yes

Add Assoc_ID,

cat_pct, pop05

and pop2020

Is there

another row? 

Yes

Change field name

minpwsid to PWSID;

Delete maxpwsid field;

Automatically adjust population served

from GIS script values

No

Ste

p 1 Ste

p

2

Ste

p

3

Ste

p

4

Ste

p

3
Methods for Estimating Water Use 17

Table 4. Sample data from the AssociationWater table for a specific census block that is modified from the geographic information system script output to its final version by step.[GIS, geographic information system; CWS, community water system; Auto, automatically; Colored entries indicate changes made during that step; Field definition for tables: STFID, Unique census block number; pop00, 2000 population count; hu00, 2000 housing unit count; minpwsid, Minimum system identification number; maxpwsid, Maximum system identification number; rds_tot, Total length of roads; rds_wat, Length of roads inside “water” areas; rds_both, Length of roads inside “both” areas; rds_sewer, Length of roads inside “sewer” areas; pct_water = (rds_water + rds_both)/rds_total; pct_sewer = (rds_sewer + rds_both)/rds_total; Assoc_ID, unique record number for the AssociationWater table; cat_pct, Percent category; pop05, 2005 population estimate; pop2020, 2020 population projection; PWSID, Public Water System identification number; Revised Category Percent Water, Whether the automatic value was adjusted; Status, Whether revision to this field was completed; Population 2000 Census Auto adjusted = 2000 population count calculated as percent category * 2000 population; Population 2005 Estimated Auto adjusted = 2005 estimated population count calculated as percent category * 2005 estimated population; Population 2020 Projected Auto adjusted = 2020 projected population count calculated as percent category * 2020 population; Population 2000 Census Manually adjusted, 2000 population count estimated for each census block; Population 2005 Estimated Manually adjusted, 2005 estimated population count estimated for each census block; Population 2020 Projected Manually adjusted, 2020 projected population count estimated for each census block]

Record as it comes from GIS processing script.

STFID pop00 hu00 minpwsid maxpwsid rds_tot rds_wat rds_both rds_sew pct_water pct_sewer

330150670001061 146 79 2232060 2232160 8201.53 4640.11 0 0 0.57 0

Step 1. Create AssociationWater table.

STFID pop00 minpwsid maxpwsid pct_water

330150670001061 146 2232060 2232160 0.57

Step 2. Add fields.

Assoc_ID STFID minpwsid maxpwsid pct_water cat_pct pop00 pop05 pop2020

28138 330150670001061 2232060 2232160 0.57 0.50 146 164 184

Step 3. Add records for self-supplied population and for maxpwsid.

Assoc_ID STFID minpwsid maxpwsid pct_water cat_pct pop00 pop05 pop2020

28138 330150670001061 2232060 2232160 0.057 0.50 146 164 184

47115 330150670001061 0 0.50 146 164 184

50810 330150670001061 2232160 146 164 184

Step 4. Calculate population served.

Assoc_ID STFID PWSID Percent on any CWS Category percent water Revised category percent water Status Population 2000 Census 2005 Estimated 2020 Projected Original Auto adjusted Original Auto adjusted Original Auto adjusted

28138 330150670001061 2232060 0.57 0.50 146 73 164 82 184 92

47115 330150670001061 0 -- 0.50 146 73 164 82 184 92

50810 330150670001061 2232160 -- -- 146 -- 164 -- 184 --

Step 5. During quality assurance, adjust the population that is self-supplied or served by specific CWS.

Assoc_ID STFID PWSID Percent on any CWS Category percent water Revised category percent water Status Population 2000 Census 2005 Estimated 2020 Projected Original Manually adjusted Original Manually adjusted Original Manually adjusted

28138 330150670001061 2232060 0.57 0.50 y Done 146 89 164 100 184 105

47115 330150670001061 0 -- 0.50 y Done 146 20 164 24 184 35

50810 330150670001061 2232160 -- -- y Done 146 37 164 40 184 44
18 Methods for Estimating Withdrawal and Return Flow by Census Block for 2005 and 2020 for New Hampshire

Quality Assurance

Step 5 in table 4 (shown in purple) shows adjustments 

made during the quality-assurance process; the details of the 

process are shown in figure 9. A query was written linking 

the AssociationWater table with a list of active CWSs from 

the Drinking Water database to compare the populationserved values from both sources. Review of the scriptassigned percent categories was needed under any of the 

following conditions:

1. There were CWSs in the AssociationWater table 

that were not in the table of active CWSs from the 

Drinking Water database; 

2. There were CWSs in the table of active CWSs from 

the Drinking Water database that were not in the 

AssociationWater table (for example, for census 

blocks with CWSs that only served populations on 

streets in the interior of the census block); and 

3. The population served values in the 

AssociationWater table were less than 80 percent or 

more than 120 percent of the corresponding reported 

values in the Drinking Water database (which 

frequently occurred when there was more than one 

CWS serving populations in the census block). 

The first test (fig. 9) was to determine whether there 

were CWSs in the AssociationWater table that were not in 

the table of active CWSs extracted from the Drinking Water 

database. When this occurred, Drinking Water Program staff 

were contacted to determine whether the inactive CWS was 

replaced by another CWS or not. If replaced, the PWSID of 

the current CWS supplying the census block was entered in 

the AssociationWater table in place of the inactive PWSID. 

If the inactive CWS was not replaced, the population became 

part of the self-supplied value.

The second test (fig. 9) was to determine whether 

there were active CWSs that were missing from the 

AssociationWater table. This could occur if a CWS was 

located on an interior road within the census block or if the 

CWS was established more recently than the GIS data set. 

The GIS script did not account for populations along streets 

interior to a census block (most commonly dead-end streets) 

that are supplied by different CWSs than those on the census 

block boundaries. This occurs primarily with small domesticonly CWSs. Inspection of the water-distribution areas in the 

GIS data set was used to identify the census blocks served 

by the CWS. In the instance where the CWS was established 

more recently than the GIS data set, the location of the CWS 

well(s) was used to identify the census blocks associated with 

the CWS. In both cases, new records were created for the 

CWS in each associated census block.

The third test (fig. 9) was to compare the estimated 

population served by each CWS to the reported value. This 

was done by dividing the automatically adjusted values 

(totaled for all census blocks served by the CWS) in the 

AssociationWater table (table 4, step 4) by the population 

served reported in the Drinking Water database. If the resulting 

ratio was less than 80 percent or more than 120 percent, all 

the census blocks associated with the CWS were evaluated. 

If any of these census blocks contained part of another CWS 

distribution system, all the census blocks associated with that 

second CWS were included in the evaluation. Ultimately, 

all CWSs and census blocks that were geographically 

interconnected with the originally selected CWS were 

identified and evaluated as a unit. An example of this situation 

using the census block included in table 4 is illustrated in 

figure 10. Table 5 provides one set of population-served 

estimates derived through this quality-assurance process.

The selected CWS from table 4, CWS 2232060, is 

associated with census blocks 330150670001061 and 

330150670001060 (fig. 10). The automatically adjusted 

population served by this CWS in 2000 totals 76 (73 people 

in 330150670001061 and, not shown in table 4, 3 people in 

330150670001060), which is 72 percent of the 105 population-served value obtained from the Drinking Water database. 

Because this ratio fails test 3 in figure 9, all associated CWSs 

and census blocks were examined (table 5). A second CWS, 

CWS 2232160, also serves people in 330150670001061. The 

GIS script calculated the proportion of the population served 

in the census block. So, for blocks with multiple CWSs, it was 

necessary to manually apportion the population served among 

all CWSs in the block. In order to do this, all CWSs that touch 

any of the census blocks associated with the selected CWS 

(2232060) were examined. This resulted in the list of all the 

CWSs and census blocks shown in table 5. 

A perimeter road of census block 330150670001061 also 

coincides with the buffered area of CWS 2232150. It is not 

likely that any people within 330150670001061 are served by 

2232150 though, because the overlap is merely an artifact of 

the buffering process. CWS 2232150 serves the interior roads 

of census block 330150670001067. The entire population 

served by that CWS (46) is attributed to 330150670001067, 

and the remainder of the population in that census block (109) 

is self-supplied. 

CWS 2232160 touches four census blocks: 

330150670001061, 330150670001062, 330150670001063, 

and 330150685002028. Neither 330150670001063 

nor 330150685002028 contain any population, and 

330150670001062 contains only population (85) served by 

CWS 2232160; therefore, the only census block requiring 

analysis is 330150670001061. The reported population from 

the Drinking Water database is 150, so the population in 

330150670001061 served by CWS 2232160 would range from 

37 (minimum to meet the goal of more than 80 percent) to 65 

(maximum, if there are enough people available who are not 

accounted for by other CWSs).

CWS 2232060 touches three census blocks: 

330150670001060, 330150670001061, and 

330150685002027. Census block 330150685002027 does not 

contain any population served by CWS 2232060. The population in parts of 330150670001060 and 330150670001061 
Methods for Estimating Water Use 19 Figure 9. Flowchart representing the quality-assurance process used to adjust population that is self-supplied or served by any community water systems in the census block.

Is

there a CWS

in AssociationWater table

with matching record

in Drinking Water

database?

No

Note that CWS is seasonal

Select CWS

Adjust population served to

Census block population and

portion of census block covered

by water distribution system

[CWS, community water system; GIS, geographic information system; PWSID, public water system identification number; <, less than; %, percent; pop, population; purple shade relates the step to that in table 4 and indicates the action step for this quality-assurance process] 

Determine census blocks

in service area based on

well location

Is there a CWS with

pop served <80%?

Examine all census blocks in

GIS data set associated with all

CWSs touching any of the

census blocks associated with

selected CWS distribution system

No

Yes

Is population

served calculated through

AssociationWater table between

80% and 120% of the reported

value in Drinking Water

database?

Active CWS table

from Drinking

Water database 

AssociationWater

table

Is this a

CWS in the interior

of the census

block?

No

Yes

Is there a

CWS in Drinking Water

database with matching record

in AssociationWater

table? 

No

No

Water Distribution

GIS data set

Test 1

Test 2

Test 3

Add new record to

AssociationWater table

Qu

ality

Assur

ance 

No

Assign valid PWSID

Add populationto self-supplied

Is

CWS still active?

(Step 5 in table 4)

Yes

Yes

Yes

Yes
20 Methods for Estimating Withdrawal and Return Flow by Census Block for 2005 and 2020 for New Hampshire

then needs to number at least 85 (minimum to meet the goal 

of more than 80 percent) and at most 105 people (maximum, 

if there are enough people available who are not accounted for 

by other CWSs). 

At this point, only two census blocks require adjustments: 

the population of census block 330150670001061 needs to be 

apportioned among CWS 2232160, CWS 2232060, and selfsupply; and the population of 330150670001060 needs to be 

apportioned between CWS 2232060 and self-supply. Because 

census block 330150670001060 contains only six people and 

there is an interior road branching off the distribution area, 

all six are assumed to be served by CWS 2232060. CWS 

2232060 needs at least 78 more people, CWS 2232160 needs 

at least 37 more people, self-supply needs some people, and 

the total cannot exceed 146. Balancing available population 

and road density in 330150670001061 yields a final breakdown of 37 people for CWS 2232160, 89 people for CWS 

2232060, and 20 people for self-supplied. Results are shown 

in table 5.

The procedure described above was used for most systems that failed test 3. Visual inspection of the spatial data was 

used to apportion the population in each census block among 

the different CWSs. On the basis of the road density in relation 

to the location of each CWS, the calculated population value 

was manually adjusted to reconcile the GIS-estimated population served with the reported population served. The previous 

assignments of census-block populations to CWSs in the New 

Hampshire Seacoast region (Horn and others, 2008) were 

incorporated into this study.

In some cases, test 3 could not be reconciled by the above 

process; that is, the estimated value could not be adjusted to 

one that was more than 80 percent of the reported value. In the 

majority of these cases, the CWS was seasonal and, therefore, 

the census population value used for the estimate did not 

reflect the summer-only population. The CWS was identified 

as seasonal.

Figure 10. Example of a suite of community water systems and census blocks that are geographically interconnected.

330150670001067

330150670001061

330150670001062

330150670001063

330150685002028

330150685002027

330150670001060

2232160

2232150

2232060

70°53' 70°52'30" 70°52' 70°51'30"

43°02'

43°01'30"

0 0.1 0.2 MILES

0 0.1 0.2 KILOMETERS

EXPLANATION

Roads on census block

boundaries

Roads that are interior to

census blocks

Census block boundaries

that are not roads

Water Distribution Areas

2232160

Census block

identification

number (STFID)

Public Water System

identification number

(PWSID)

330150685002028

Water Distribution Areas from New Hampshire Department of Environmental Services, 2003

Roads and block boundaries from U.S. Census Bureau, 2006

New Hampshire State Plane Coordinate System, North American Datum 1983
Methods for Estimating Water Use 21

Table 5. Quality-assured estimates of population served for a suite of interconnected community water systems and census blocks.[CWS, community water system; Auto, automatically; yellow, orange, and purple shades refer to the steps in table 4; gray shade highlights the manually adjusted values]

Census block identifier

Total census 

block 

population

Population served Total manually 

adjusted population CWS 2232060 CWS 2232150 CWS 2232160

Auto adjusted Manually adjusted Auto adjusted Manually adjusted Auto adjusted Manually adjusted CWS-served Self-supplied

330150670001060 6 3 6 6 0330150670001061 146 73 89 0 0 0 37 126 20330150670001062 85 85 85 85 0330150670001063 65 16 0 0 65330150670001067 155 0 46 46 109330150685002027 56 0 0 0 56330150685002028 43 0 0 0 43

Total from AssociationWater table 556 76 95 0 46 101 122 263 293Total from Drinking Water database 105 105 46 46 150 150 301Ratio, in percent 72 90 0 100 67 81 87
22 Methods for Estimating Withdrawal and Return Flow by Census Block for 2005 and 2020 for New Hampshire

Estimation of Water Use by Census Block

The amounts of water demand, consumptive use, withdrawal, and return flow were estimated for 2005 and projected 

for 2020. Estimates of water demand and associated consumptive use were made using reported data from registered users 

and relations between water demand and ancillary data sets 

(Horn and others, 2008). These estimates of water demand 

served as the basis for estimates of groundwater and surfacewater withdrawal. Estimates of return flow were calculated 

as water demand minus consumptive use. Projected population growth rates from 2000 to 2020 were applied in order 

to extend the water-use estimates to 2020 (New Hampshire 

Office of Energy and Planning, 2007b).

To estimate water demand where reported use or metered 

delivery data were not available, the relations between water 

demand and ancillary data were studied. In some cases 

(domestic and industrial use), this relation is expressed as a 

water-use coefficient. A water-use coefficient is an amount 

of water used per unit (for example, per person, household, 

or employee) and is multiplied by the number of units at the 

facility or within the area to obtain the total water demand for 

that facility or area. For example, if the domestic per capita 

water-demand coefficient is 75 gal/d and there are 1,000 

people in the census block, the total domestic water demand 

is 75,000 gal/d in the census block. Coefficients are developed by analyzing the statistical relation between reported or 

metered water demand and ancillary data, such as population 

per housing unit, median value of homes, population density, 

number of employees at a specific facility, or units of product. 

To estimate commercial demand, a facility demand rate was 

developed through an analysis of the manner in which the 

water is used and the general size of the facility. 

Assumptions

The following assumptions were made to estimate 2005 

and 2020 water use: 

• The 75 gal/d per capita and 16 percent consumptiveuse coefficients derived during the Seacoast water-use 

study (Horn and others, 2008) can be applied to the 

entire State to estimate domestic withdrawal and 

return flow. 

• The 2000 to 2005 and 2000 to 2020 town growth rates 

can be applied to each census block within the town 

to yield 2005 and 2020 population estimates for each 

census block appropriate for aggregating to larger 

geographic areas.

• The source of water and method of wastewater disposal 

do not change over time for any census block; that is, 

the same ratio of self-supplied to public supply is used 

for 2000, 2005, and 2020.

• Unregistered commercial and industrial self-supplied 

users that are outside the boundaries of CWWS collection systems as defined in the Water Distribution and 

Sewer Collection data set have on-site disposal; those 

that are inside the boundaries release wastewater into 

the collection system. 

• The rate of water demand and consumptive use per 

person does not change over time; that is, coefficients 

developed for 2003 (Horn and others, 2008) are applicable for 2005 and 2020 estimates.

• Commercial water demand will increase at the same 

rate as domestic water demand in a census block; that 

is, commercial demand is tied to estimated population 

growth rates. 

• Industrial water demand will not increase from 2005 

to 2020 because increased industrial activity will be 

offset by more efficient use of water by new industries.

• Hydroelectric, thermoelectric, and irrigation demand 

for 2020 will be the same as 2005 reported values.

2005 Registered Use

Reported water withdrawal and return-flow data for 

2005 for registered non-domestic users and most multi-use 

CWSs are stored in the WATUSE database. These data were 

integrated with the Drinking Water tables in the NH Water 

Demand database. The withdrawal values were linked to 

specific wells and surface-water intake pipes, and return-flow 

values were linked to discharge pipes. In some cases, it was 

necessary to estimate withdrawal values from specific wells 

or surface-water intakes because the reported withdrawal was 

for combined sources. These estimates were based on the 

total reported withdrawal divided evenly among all sources 

included in the reported total. Each source and discharge location was then associated with a census block in order to sum 

these water-use values and the estimates for unregistered users 

in each block.

2005 Unregistered Use

Domestic and non-domestic water withdrawal and 

return flow by unregistered users were estimated using two 

different approaches. Domestic water withdrawal estimates 

were based on the per capita water-demand coefficient applied 

to the portion of the population on self-supply. Estimates of 

domestic water return flow were calculated by subtracting 

the consumptive-use coefficient from the per capita demand 

coefficient and applying this coefficient to the portion of the 

population with on-site waste disposal. A different approach 

was required for estimating unregistered non-domestic water 

use due to the large variation in types of users. Non-domestic 

water withdrawal and return-flow estimates were based on 

water-demand and consumptive-use coefficients specific to the 

type of user. 
Methods for Estimating Water Use 23

Domestic Water Withdrawal and Return Flow

There are two types of domestic users: those that are 

self-supplied and those that are served by a small domesticonly CWS. The procedures for estimating the withdrawal by 

a domestic-only CWS are similar to those for self-supplied 

users, except for an additional step to link the total withdrawal 

for the system to the wells and surface-water intake pipes 

identified in the Drinking Water database.

Self-supplied domestic withdrawal in 2005 was estimated 

by multiplying the self-supplied population in each census 

block (estimated using the GIS script and quality-assurance 

adjustments) by the 75 gal/d domestic-demand coefficient 

from Horn and others (2008). Return flow for each census 

block was estimated using the estimated 2005 population 

with on-site waste disposal and the 63 gal/d domestic-return 

coefficient, derived by subtracting the 16 percent attributed to 

consumptive use from the demand (Horn and others, 2008).

An illustration of self-supplied withdrawal is shown 

as an example in figure 11. Each census block is classified 

according to the estimated self-supplied domestic withdrawal 

(in gal/day) divided by the size of the census block (in mi2) 

to provide an indication of the intensity of the withdrawal in 

that area. A census block could have no self-supplied domestic 

withdrawals because there are no people living there, or 

because 100 percent of the census block population is 

publicly served.

Withdrawal by each small domestic CWS was estimated using the 75 gal/d water-demand coefficient and the 

estimated CWS 2005 population to compute a total demand 

for the CWS. The CWS demand was divided among all of its 

withdrawal points, and the withdrawal estimate was linked to 

the point(s). Each withdrawal location was associated with a 

census block by using its latitude and longitude coordinates. 

All return flow from the small CWS was assumed to be onsite waste disposal and included in the census-block total for 

return flow.

Non-Domestic Water Withdrawal and Return Flow

Non-domestic water withdrawal and return flow were 

estimated by assigning every non-domestic user to a wateruse group that represents users with similar water-use 

characteristics. For any unregistered users, water demand 

can be estimated using a coefficient (for example, the food 

industry uses 469 gal/employee/day) or can be estimated per 

facility (for example, a small restaurant uses 1,000 gal/d). 

The water demand for each user was divided among and 

associated with the known withdrawal points. The return flow 

was estimated as 90 percent of the water demand and was 

collocated with the withdrawal site. 

In order to characterize water demand, each of the 2,424 

public water systems in the State was categorized into a wateruse group related to Standard Industrial Classification (SIC) 

code. Determination of the appropriate water-use group for 

individual users was based initially on the user name. When 

the name of the facility alone did not allow for a water-use 

group assignment, a search of the Internet often provided 

sufficient information to categorize the facility. For example, 

“Colley McCoy” and “1 Industrial Dr, Wyndam” yielded an 

Internet description that made it clear that this is a restaurant. 

There are 753 facilities (such as apartments, nursing homes, 

mobile home parks and others) categorized as community 

water systems (water-use group code 4941). Water demand 

was estimated using the 75 gal/d coefficient for any CWS that 

did not report its use. The 54 industrial facilities were grouped 

by 2-digit SIC code into 20 categories (table 6). The 1,617 

commercial facilities were divided into 12 water-use groups 

(table 7). 

Water-demand coefficients for the facilities in the 

industrial water-use groups in table 6 were developed by 

Planning and Management Consultants, Ltd. (1995) on the 

basis of water-meter readings at individual industrial facilities 

across the Nation (Horn and others, 2008). The range, median, 

and mean of these national coefficients and the number of 

facilities in NH in each category are shown in table 6.

Water demand for each of the 12 commercial water-use 

groups was estimated on the basis of facility size and types of 

activities (table 7). Commercial establishments with metered 

delivery data were grouped and subdivided by natural breaks 

in the magnitudes of meter readings. Specific water-related 

activities were identified that were likely responsible for the 

natural groupings, such as whether a school has a pool and 

whether a hotel has a restaurant. The unmetered commercial 

facilities were then grouped by general description (for 

example, hotels) and subgrouped by identifying the specific 

activities occurring at the facility (for example, hotels with 

restaurants). The median water demand values for the 

metered establishments in each subgroup were rounded and 

used for all commercial facilities in that subgroup (Horn and 

others, 2008). 

2020 Projections

The amounts of water demand, consumptive use, withdrawal, and return flow by census block were estimated for 

2020 in a manner similar to that used to estimate the 2005 values. Estimates of 2020 water use were based on the 2005 estimates or reported values and the projected population growth 

rates for 2020 for domestic and commercial demand. Industrial, hydroelectric, thermoelectric, and irrigation demand were 

assumed to remain constant. (See “Assumptions” section). 

Withdrawal and return flow were estimated for 2020 by 

census block for self-supplied domestic users and domestic 

CWS users with the same methods used to estimate the 2005 

values. The self-supplied and CWS-served populations 

within each census block were updated on the basis of the 

2020 population projections, and withdrawal and return flow 

values were estimated on the basis of the 75 and 63 gal/d 

coefficients, respectively.

Non-domestic water withdrawal and return flow 

were estimated by increasing each commercial facility’s 

2005 demand by the town growth rate from 2005 to 2020. 
24 Methods for Estimating Withdrawal and Return Flow by Census Block for 2005 and 2020 for New Hampshire

Figure 11. The intensity of self-supplied domestic withdrawal estimated by census block for 2005 in 

New Hampshire.

72°

71°

45°

44°

43°

EXPLANATION

Lake

Self-supplied domestic withdrawal

estimated by census block for 2005

0

1–2,500

2,501–10,000

Greater than 10,001

0 10 20 MILES

0 10 20 KILOMETERS

(in gallons per day per square mile)

Census block spatial data from U.S. Census Bureau, 2006

New Hampshire State Plane Coordinate System, North American Datum 1983
Methods for Estimating Water Use 25

Table 6. Coefficients for estimation of industrial water demand from two-digit Standard Industrial Classification 

categories and number of employees.

[Nonresidential employee water-demand coefficients are from Planning and Management Consultants, Ltd., 1995. --, no data available]

Two-digit Standard Industrial Classification 

category and [code]

Nonresidential employee water-demand coefficient 

(gallons per employee per day) Number of facilities 

in New Hampshire

Range Median Mean

Industrial [20–39] 21–2,160 116 297 --

Food [20] 96–677 469 419 15

Tobacco [21] -- -- 217 0

Textile mill products [22] 246–1,076 315 521 1

Apparel [23] 6–43 13 21 0

Lumber and wood [24] 32–109 78 72 4

Furniture [25] 25–65 30 37 1

Paper [26] 114–8,304 863 2,160 3

Printing [27] 15–66 42 40 5

Chemicals [28] 128–653 289 363 3

Petroleum [29] 278–1,437 1,045 920 0

Rubber [30] 73–170 119 119 4

Leather [31] -- -- 148 0

Stone, clay, glass, and concrete [32] 13–224 202 147 1

Primary metal [33] 87–424 178 186 2

Fabricated metal [34] 48–585 95 189 2

Machinery [35] 28–153 58 70 7

Electrical equipment [36] 30–169 71 112 1

Transportation equipment [37] 14–143 63 78 1

Instruments [38] 40–141 66 72 3

Jewelry, precious metals [39] 27–61 36 39 1
26 Methods for Estimating Withdrawal and Return Flow by Census Block for 2005 and 2020 for New Hampshire

Table 7. Commercial facility water-demand estimates by water-use group.

[gal/day, gallons per day]

Water-use 

group code

Water-use group 

description

Population served 

range

Facility waterdemand estimates 

(gal/day)

Number of 

facilities Comments

5300 Retail stores 25–36 250 5 Population served reflects employees, not customers.

43–70 500 4

40 750 1

125–173 1,000 3

200 1,500 1

400 2,500 1

5411 Grocery stores 25–225 500 88 Facility water-demand value related to population served; 

population served for smaller numbers reflect employees 

rather than customers.

250–999 1,000 25

30–395 2,000 7

5812 Restaurants 25–250 500 106 Facility water-demand values are not based entirely on population served, as the population may mean those served 

during an hour, or over the course of a day. Other factors 

include whether the restaurant is seasonal or year round; sit 

down or take out.

25–500 1,000 122

100–400 1,500 17

300–1,500 2,000 35

300–1,000 2,500 6

7011 Motels and inns 25–138 500 113 Facility water-demand value related to population served, 

whether the facility has a restaurant, a pool, and (or) 

jacuzzis.

30–50 1,000 3

48–300 1,500 26

115–5,000 2,500 5

7032 Campgrounds and 

youth recreational 

camps

25–183

15–657

55–650

665–1,350

250

500

1,000

1,500

96

212

78

4

Facility water-demand value primarily related to water-using 

facilities available, the population served, and seasonal 

activity.

7600 Businesses 25–35 250 15 Facility water-demand value related to population served.

35–60 500 36

60–75 750 10

75–600 1,500 26

7800 Recreational facilities 20–2,500 250 64 Facility water-demand value primarily related to water-using 

facilities available, the population served, and seasonal 

activity.

25–900 500 32

25–800 1,000 25

150–1,500 1,500 22

450–4,500 3,000 4

7997 Golf courses 25 500 1 Facility water-demand value related to water-using facility 

available: snack bars, restaurants, showers, and irrigation 

systems.

25–150 1,000 11

100–120 1,500 3

200 2,000 1

25–300 Reported 25

8059 Health care facilities 40–50 500 3 Facility water-demand value related to population served.

53–76 1,000 4

100–247 2,000 5

8062 Medical offices and 

hospitals

25–70

1,000

500

3,000

10

1

Facility water-demand value related to population served.

8211 Schools and day cares 20–98 250 148 Facility water-demand value related to population served.

60–85 500 3

99–325 1,000 82

335–730 2,000 56

750–2,500 6,000 19

9000 Offices 15–49 500 32 Facility water-demand value related to population served.

50–90 750 18

100 1,000 2

1,053 2,500 1
Summary 27

Projected trends in commercial water demand were assumed 

to be strongly related to projected trends in domestic water 

demand—an increase in population leads to an increase in the 

commercial services needed for the population. Changes in 

CWS withdrawal and CWWS return flow from 2005 to 2020 

were assumed to occur in proportion to the changes in projected population served as well. In the absence of data to indicate an increase or decrease in future demand, no change in 

industrial, irrigation, and other non-commercial demand was 

projected. It would be reasonable to assume that water demand 

associated with any increase in non-domestic, non-commercial 

activity likely will be offset by more efficient use of water by 

new facilities. The 2020 water demand for each non-domestic 

user was divided by the number of sources and associated 

with each withdrawal point. The return flow was estimated as 

90 percent of the water demand and was collocated with the 

withdrawal site.

The increase in commercial demand probably will 

not occur as a growth-rate increase at each facility nor as 

a growth-rate increase within the census block. However, 

the growth-rate increase will likely occur at the town level 

or watershed level, depending on the size of the watershed. 

Therefore, the increase in commercial demand projected for 

each census block will not be as accurate as the commercial 

demand aggregated over a larger geographic area.

Summary

Methods were developed to estimate water use for 2005 

and to project water use for 2020 throughout the State of 

New Hampshire by census block. The project was conducted 

by the U.S. Geological Survey, in cooperation with the 

New Hampshire Department of Environmental Services 

(NHDES), as part of a statewide study by NHDES relating 

water use to water availability. Estimates of water use rely on 

understanding what affects water demand and the associated 

consumptive use. The quantity of water needed for specific 

activities (demand) determines the quantity that is withdrawn, 

and the quantity of water that is returned to the hydrologic 

system after use depends on the quantity that is evaporated or 

otherwise removed from the system.

Water users in New Hampshire were identified using a 

combination of State and Federal data, which were integrated 

into the New Hampshire Water Demand database created 

for this study. The State databases yielded information on 

registered users, unregistered self-supplied non-domestic 

users, community water and wastewater systems (including 

population served and locations of points of supply and return 

flow), and population projections. Additional information on 

the size and type of unregistered self-supplied non-domestic 

users was obtained from the Internet. Domestic water users 

were enumerated and located using U.S. Census Bureau data 

for 2000, including census block population and housing-unit 

counts, census block boundaries, and roads. 

Areas where withdrawal and return flow occur were 

determined by identifying the source of water and destination 

of wastewater for each user. The water source and disposal 

type were available in the State databases for non-domestic 

users but not for domestic users. Instead, water source and 

disposal type were determined for domestic users by comparing a data set from NHDES showing Water Distribution and 

Sewer Collection Areas to U.S. Census Bureau population 

and roads data. An algorithm was developed to automatically 

estimate the percentage of the population in each census block 

served by community water systems and the percentage served 

by sewers. The remaining portions were assumed to be selfsupplied and have on-site disposal, respectively. All percentages were multiplied by the 2000 population, the estimated 

2005 population, and the projected 2020 population in each 

census block. Manual adjustments of the estimates were made 

during the quality-assurance process. Summary tables of this 

withdrawal and return information are included in the New 

Hampshire Water Demand database.

The amounts of water demand and consumptive use 

for 2005 were estimated using data from the State database 

of registered users and results from a previous study in the 

Seacoast region of New Hampshire. The domestic-demand 

coefficient of 75 gallons per day from the Seacoast study was 

applied to individual users and unregistered domestic-only 

community water systems. Every non-domestic user was 

assigned to a water-use group representing users with similar 

water-use characteristics. Estimates of water demand for each 

commercial facility group developed during the Seacoast 

study were refined, and employee water-demand coefficients 

developed by Planning and Management Consultants, Ltd. 

were applied to each industrial facility by category. On the 

basis of these assessments, estimates of withdrawal and return 

flow were derived for the State. Projected population growth 

data from the State were used to develop a growth rate that 

was applied to domestic and commercial demand to extend the 

2005 estimates to 2020. 
28 Methods for Estimating Withdrawal and Return Flow by Census Block for 2005 and 2020 for New Hampshire

References Cited

Horn, M.A., 2002, User’s manual for the New England 

water-use data system (NEWUDS): U.S. Geological 

Survey Open-File Report 01–328, 377 p. (Available at 

http://pubs.water.usgs.gov/ofr01-328).

Horn, M.A., Moore, R.B., Hayes, Laura, and Flanagan, S.M., 

2008, Methods for and estimates of 2003 and projected 

water use in the Seacoast Region, southeastern New 

Hampshire: U.S. Geological Survey Scientific Investigations Report 2007–5157, 87 p., plus 2 appendixes on CDROM (Available at http://pubs.usgs.gov/sir/2007/5157).

New Hampshire Department of Environmental Services, 

2006, Scope of the NPDES Program: NHDES Environmental Fact Sheet WD–WEB–21, 5 p. (Available at 

http://des.nh.gov/organization/commissioner/pip/factsheets/

wwt/documents/web-21.pdf).

New Hampshire Geological Survey, 2007, Water use registration and reporting in New Hampshire: New Hampshire 

Department of Environmental Services Environmental 

Fact Sheet CO–GEO–4, 2 p. (Available at http://des.nh.gov/

organization/commissioner/pip/factsheets/geo/documents/

geo-4.pdf).

New Hampshire Office of Energy and Planning, 2007a, 2005 

Population estimates of New Hampshire cities and towns, 

accessed January 11, 2007, at http://www.nh.gov/oep/

programs/DataCenter/Population/PopulationEstimates.htm.

New Hampshire Office of Energy and Planning, 2007b, 

2010–2030 Population projections for New Hampshire 

municipalities, accessed January 11, 2007, at 

http://www.nh.gov/oep/programs/DataCenter/Population/

PopulationProjections.htm.

Planning and Management Consultants, Ltd., 1995, IWRMAIN Water demand analysis software, User’s manual and 

system description, version 6.1: Carbondale, Ill., 497 p.

U.S. Census Bureau, 2001, Census block demographics 

Summary File 1 (SF1) for New Hampshire, accessed 

September 17, 2003, at http://arcdata.esri.com/data/

tiger2000/tiger_download.cfm.

U.S. Census Bureau, 2006, 2006 Second Edition TIGER/Line 

Files, accessed December 15, 2006, at http://www.census.

gov/geo/www/tiger/tiger2006se/tgr2006se.html.

U.S. Census Bureau, 2007, 2006 Second Edition TIGER/

Line Files Technical Documentation: Washington, D.C., 

353 p. (Available at http://www.census.gov/geo/www/tiger/

tiger2006se/TGR06SE.pdf).

U.S. Environmental Protection Agency, 1998, SDWA Section 

1401(4) Public Water System Definition as Amended by 

1996 SDWA Amendments: Federal Register, v. 63, no. 150, 

Notice, p. 41939–41946, accessed January 5, 2006, at 

http://www.epa.gov/safewater/pws/pwsfrn.html.
Glossary 29

Glossary

D

Delivery The amount of water delivered to 

users.

Discharge pipe A pipe through which 

effluent is released after use into a receiving 

stream or infiltration bed. Also referred to as 

an outfall.

Distribution The process of conveying 

water from the community water-system 

points of withdrawal or treatment through 

the distribution system to the user or another 

water supplier. Water is “released” from the 

community water system into the distribution 

systems and “delivered” to users. See also

Delivery and Release. 

Distribution system A pipe or system of 

pipes conveying water from wells and intake 

pipes or a potable water-treatment plant to 

users. A local distribution system conveys 

water to users within a single minor civil 

division. A regional distribution system 

conveys water to users in more than one 

minor civil division or to another regional 

distribution system.

Domestic self-supplied withdrawal 

estimate For this statewide study, the 

population within a census block that is selfsupplied was multiplied by the average annual 

per capita water demand (75 gallons per day) 

derived from the Seacoast water-use study.

Domestic septic return flow estimate For 

this statewide study, the population within a 

census block that uses a septic system was 

multiplied by the average annual per capita 

water demand (75 gallons per day, derived 

from the Seacoast water-use study); then 

the amount of consumptive use (16 percent, 

derived from the Seacoast water-use study) 

was subtracted.

Domestic water use Water for household 

purposes, such as drinking, food preparation, 

bathing, washing clothes and dishes, flushing 

toilets, and watering lawns and gardens. 

Households include single and multi-family 

dwellings. Also called residential water 

use. The water may be obtained from a 

community water system or be self-supplied.

A

Aggregate of users A group of users defined 

by a geographic area, such as state, county, 

minor civil division, or Hydrologic Unit 

boundary, for which withdrawal, distribution, 

use, consumptive use, wastewater collection, 

or return flow are collectively estimated.

C

Census block The smallest geographic 

area for which the U.S. Census Bureau 

collects and tabulates data. A census tract is 

subdivided into census block groups, which 

are subdivided into blocks.

Coefficient See water-use coefficient.

Commercial water use Water used for 

motels, restaurants, office buildings, ski 

resorts, water parks, and other commercial 

facilities and institutions. The water may be 

supplied by a community water system or be 

self-supplied.

Community wastewater system 

(CWWS) Wastewater collected from users 

or groups of users, conveyed to a wastewatertreatment plant and released as return flow 

into the hydrologic environment or sent back 

to users as reclaimed wastewater. 

Community water system (CWS) System 

for the provision to the public of water for 

human consumption through pipes or other 

constructed conveyances if such a system 

has 15 year-round service connections or 

serves more than 25 year-round residents. 

Community water systems provide water 

for a variety of uses, such as domestic, 

commercial, industrial, thermoelectric power, 

and public use. 

Consumptive use That part of withdrawn 

water that is evaporated, transpired, incorporated into products or crops, consumed by 

humans or livestock, or otherwise removed 

from the immediate water environment.

Conveyance The systematic and intentional 

flow or transfer of water from one point to 

another primarily during distribution and 

wastewater collection.
30 Methods for Estimating Withdrawal and Return Flow by Census Block for 2005 and 2020 for New Hampshire

E

Export Water that is removed from an area 

(watershed or town) for use in another area, 

or wastewater that is removed after use from 

an area (watershed or town) for treatment and 

release in another area.

G

Geographic information system (GIS)

A computer system capable of capturing, 

storing, integrating, analyzing, and displaying 

geographically referenced information.

Groundwater return flow Wastewater that 

is returned to groundwater over a geographic 

area by an aggregate of users or through 

septic systems.

Groundwater withdrawal Water that 

is withdrawn from groundwater over a 

geographic area by an aggregate of users or 

by a single user for which there is not enough 

information to select a more specific site type.

I

Import Water that enters or is brought 

into an area (watershed or town) for use, or 

wastewater that is conveyed after use from an 

outside area (watershed or town) for treatment 

and release in the area of interest.

Industrial water use Water used for 

industrial purposes, such as fabrication, 

processing, washing, in-plant conveyance, 

and cooling, and includes such industries 

as steel, chemicals, paper, and petroleum 

refining. The water may be supplied by a 

community water system or be self-supplied.

Intake pipe A pipe in a surface-water body 

through which water is diverted to another 

site.

Interbasin transfer Conveyance of water 

across a drainage or river-basin divide. 

Irrigation water use The artificial 

application of water to lands to assist in 

the growth of crops or pasture including 

greenhouses. Irrigation water use also may 

include application of water to maintain 

vegetative growth in recreational lands, such 

as parks and golf courses, including water 

used for frost and freeze protection of crops.

L

Leakage Water that moves from a 

conveyance system or storage area into the 

surrounding and underlying materials. This 

process will occur if the ambient groundwater 

pressure is less than the internal pressure of 

the conveyance system or storage area at 

a breach.

M

Mining water use Water used for the 

extraction of naturally occurring minerals 

including coal, ores, petroleum, and natural 

gas. Includes water associated with quarrying, 

milling, and other onsite activities done as 

part of mining. Excludes water used for 

processing, such as smelting and refining, or 

slurry pipeline (industrial water use). These 

activities are included in Standard Industrial 

Classification (SIC) codes 10–14.

Minor Civil Division A political or 

administrative area of a county or county 

equivalent, other than an incorporated place, 

established by appropriate state or local 

government authorities and adopted as a 

primary county division; equivalent to a town 

in New England.

N

Non-community Water System (NCWS)

A water system that serves people either 

temporarily in residence (transient), as at a 

motel or restaurant, or regularly using the 

drinking-water supply without actually living 

at the site (nontransient), as at a business. 

P

Per capita water use The average volume 

of water used per person during a standard 

time period, generally per day. 

Potable treatment plant A site that prepares 

water to drinking-water standards through 

processes including chlorination, fluoridation, 

and filtration.

Projected water demand Estimates of future 

water demand generated using estimates of 

future population or employee number and 

current (2003) water-demand coefficients.

Public use Water supplied from a 

community water system and used for 

firefighting, street washing, water-treatment 

plant backflushing of filters, and municipal 

parks and swimming pools. 
Glossary 31

R

Registered user In New Hampshire, a user 

who withdraws, receives, or uses water or 

releases or returns wastewater at a rate of 

20,000 gallons per day or more over any 

7-day period.

Release Water discharged by a user or 

group of users into a wastewater-collection 

system.

Resource Aquifer or surface-water body 

from which water is withdrawn/diverted or 

returned.

Return flow Water that is returned to 

surface-water or groundwater resources 

after use or wastewater treatment and, thus, 

becomes available for reuse. Return flow 

can go directly to surface water, directly to 

groundwater through an injection well or 

infiltration bed, or indirectly to groundwater 

through septic systems. S

Self-supplied water Water withdrawn from 

a groundwater or surface-water source by 

a user and not obtained from a community 

water system.

Sewage disposal (septic) system Refers 

to a buried tank for the separation of solids, 

grease, and liquid components of wastewater 

in the absence of oxygen. The liquid fraction 

from the septic tank is discharged to a drain 

field and the solids remain in the tank for later 

disposal as septage.

Single user An individual user for which 

withdrawal, use, consumptive use, or return 

flow are measured or estimated. This place of 

use can be a manufacturing plant, commercial 

facility, or irrigation field.

Standard Industrial Classification (SIC) 

code Four-digit codes established by the 

U.S. Office of Management and Budget and 

used in the classification of establishments by 

type of activity in which they are engaged.

Surface-water return flow Wastewater that 

is returned directly to an unknown surfacewater body or wetland, or occurs over an 

area such as from irrigation or meltwater 

after snowmaking. This does not include 

water discharged into ponds for holding or 

percolation purposes.

Surface-water withdrawal Water that 

is withdrawn from surface water over a 

geographic area by an aggregate of users or 

by a single user for which there is not enough 

information to select a more specific site type. T

Transfer See water transfer or interbasin 

transfer. U

Unaccounted-for water Water supplied 

from a community water system that has 

not been accounted for as being distributed 

to domestic, commercial, industrial, or 

thermoelectric uses. It includes public water 

use (fire fighting, street washing, watertreatment plant backflushing of filters, and 

municipal parks and swimming pools), 

leakage (conveyance loss), and meter errors.

Unregistered CWS withdrawal 

estimate For this statewide study, the 

population served by the CWS was multiplied 

by the average annual per capita water 

demand (75 gallons per day) derived from the 

Seacoast water-use study.

Unregistered user In New Hampshire, a 

user who withdraws, receives, or uses water 

or releases or returns wastewater at a rate of 

less than 20,000 gallons per day over any 

7-day period. W

Wastewater Water that carries wastes from 

homes, businesses, and industries; a mixture 

of water and dissolved or suspended solids.

Wastewater collection The process of 

conveying wastewater from users through a 

wastewater-collection system (sewer system) 

to a wastewater-treatment facility. May also 

include storm runoff. Wastewater is released 

by the user into the collection system and 

received by the treatment facility. Wastewater 

also can be released from a local collection 

system into a regional collection system.

Wastewater-collection system A pipe or 

system of pipes conveying wastewater from 

users to a wastewater-treatment plant. A local 

collection system conveys wastewater from 

users within a single minor civil division. 

A regional collection system conveys 

wastewater from users in more than one 

minor civil division or from another regional 

collection system.
32 Methods for Estimating Withdrawal and Return Flow by Census Block for 2005 and 2020 for New Hampshire

Wastewater-treatment plant Plant that 

prepares wastewater for discharge into the 

hydrologic system through the removal 

or reduction of contained solids or other 

undesirable constituents.

Water demand (1) Water required to 

meet specific water-use needs, such as for 

domestic, commercial, or industrial purposes. 

The term is used in this report in connection 

with projections of current use into the future. 

(2) Relation between water use and price, 

when all other factors are held constant; that 

is, increased prices result in decreased water 

use. (3) Demand is a general concept used 

by economists to denote the willingness 

of consumers or users to purchase goods, 

services, or inputs to production processes, 

because the willingness varies with the price 

of the thing being purchased. (4) Refers to the 

schedule of water quantities that consumers 

would use per unit of time at a particular price 

per unit. 

Water supply All the processes that are 

involved in obtaining water for the user before 

use, including withdrawals, water treatment, 

and distribution.

Water transfer Artificial conveyance of 

water from one area to another. 

Water use Water use pertains to human 

interaction with and influence on the 

hydrologic cycle and includes activities such 

as water withdrawal, distribution, consumptive 

use, treatment, wastewater collection, and 

return flow.

Water-use coefficient An amount of water 

used per unit (for example, per person, household, or employee) for each category of use.

Withdrawal The removal of surface water 

or groundwater from the natural hydrologic 

system for use, including community water 

systems, industry, commercial, domestic, 

irrigation, livestock, thermoelectric power 

generation, mining, and other off-channel 

water uses.
Prepared by the Pembroke Publishing Service Center.

For more information concerning this report, contact:

Director

U.S. Geological Survey

New Hampshire-Vermont Water Science Center

331 Commerce Way, Suite 2

Pembroke, NH 03275

dc_nh@usgs.gov

or visit our Web site at:

http://nh.water.usgs.gov
Hayes and Horn—Methods for Estimating Withdrawal and Return Flow by Census Block for 2005 and 2020 for New Hampshire—Open-File Report 2009–1168

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