Residential End Uses of Water Study (1999)

The Residential End Uses of Water study (REUWS) published in 1999 by the AWWA Research Foundation and the American Water Works Association is a research study that examined where water is used in single-family homes in North America.  Conducted by Aquacraft, PMCL, and John Olaf Nelson, the REUWS was the largest study of its kind to be completed in North America and efforts are underway to repeat the effort and obtain updated results (October 2012 progress report and interim results can be viewed here).  The “end uses” of water include all the places where water is used in a single-family home such as toilets, showers, clothes washers, faucets, lawn watering, etc.  The full REUWS final report is available to the public at no charge from the Water Research Foundation (WRF).

Research Summary

Where is water used in single-family residences?  What is the volume of water that is used for toilets, showers, clothes washers, faucets, dishwashers, and all other purposes?  Does water use vary across single-family homes and across different cities and regions?  What factors influence single-family residential water use?  What is the impact of more efficient fixtures on residential demands?  The REUWS attempted to answer these and other questions about residential water consumption patterns.

Objectives

The American Water Works Association Research Foundation (AWWARF), now known as the Water Research Foundation (WRF), and 22  municipalities, water utilities, water purveyors, water districts, and water providers funded this study.  The goals of this research included:

  • Providing specific data on the end uses of water in residential settings across the continent.
  • Assembling data on disaggregated indoor and outdoor uses.
  • Identifying variations in water used for each fixture or appliance according to a variety of factors.
  • Developing predictive models to forecast residential water demand.

The 1999 REUWS report represents a time and place snapshot of how water is used in single-family homes in twelve North American locations.  Similarities and differences among "end uses" were tabulated for each location, analyzed, and summarized.  Great care was taken to create a statistically significant representative sample of customer for each of the twelve locations.  However, these twelve locations are not statistically representative of all North American locations.   A total of 1,188 individual households spread across 12 sites and 14 municipalities in the U.S. (12) and Canada (2) were studied for this project.

Two major contributions of this study are (1) demonstrating the feasibility of identifying and measuring the different ways households use water; and (2) describing and analyzing variations in water used for specific purposes between different households.

Methods

The 12 study sites were:  Boulder, Colorado; Denver, Colorado; Eugene, Oregon; Seattle, Washington; San Diego, California; Tampa, Florida; Phoenix, Arizona; Tempe and Scottsdale, Arizona; the Regional Municipality of Waterloo, Ontario; Walnut Valley Water District, California; Las Virgenes Municipal Water District, California; and Lompoc, California.

Data collected from each study site included:

  • Historic billing records from a systematic random sample of 1,000 single-family detached residential accounts;
  • Household level information obtained through a detailed mail survey sent to each of the selected 1,000 households;
  • Approximately four weeks of specific data on the end uses of water collected from a total of 1,188 households (approximately 100 per study site), data collection was divided into two, two-week intervals spaced in time to attempt to capture summer (peak) and winter (off-peak mostly indoor water use) time frames;
  • Supplemental information including climate data and information specific to each participating utility.

Water consumption for various end uses was measured using Meter-Master data loggers and Trace Wizard Water Use Analysis Software.  A flow trace is a record of flow through a residential water meter recorded in 10 second intervals which provides sufficient resolution to identify the patterns of specific fixtures within the household via signal processing techniques.  The flow trace analysis software disaggregates this virtually continuous flow trace into individual water use events such as a toilet flush or clothes washer cycle and then an analyst implements signal processing tools to assign fixture designations to each event. 

The data assembled for the REUWS included:

  • A sizable residential water use database containing nearly one million individual  water use “events” collected from 1,188 residences in the 12 study sites;
  • Household level information obtained through the mail survey completed by approximately 6,000 households
  • Historic water billing records from 12,000 residences. 

In addition to presenting the findings from the data collection effort, the project team also developed predictive models which incorporated the detailed end use information and household level socioeconomic data.

Key Assumptions

A research study of this magnitude must rely on a variety of assumptions which are taken as "givens".  It is recognized that changes in some of these assumptions could impact the results, but the limits of the project scope and funding did not allow exploration of some of the following factors:

  • The accuracy of the billing consumption histories provided by participating utilities
  • The accuracy of mail survey responses
  • The timeframe of monitoring capturing "representative" indoor water use for each home
  • Capturing the precise weather related use within the monitoring timeframe needed to analyze the variables associated with outdoor use

Findings

Annual Use

Average annual water use, based on historic billing records from approximately 1,000 accounts in each of the 12 study sites, ranged from 69,900 gallons per household per year in Waterloo and Cambridge, Ontario to 301,100 gallons per household per year in Las Virgenes MWD.  The mean annual water use for the 12 combined sites was 146,100 gallons per household per year with a standard deviation of 103,500 gallons and a median of 123,200 gallons (n=12,075).  Across all study sites 42 percent of annual water use was for indoor purposes and 58 percent for outdoor purposes.  This mix of indoor and outdoor was strongly influenced by annual weather patterns and, as expected, sites in hot climates like Phoenix and Tempe and Scottsdale had a higher percentage of outdoor use (59 – 67 percent) while sites in cooler, wetter  climates like Seattle and Tampa and Waterloo had much lower percentages of outdoor use (22 – 38 percent).  The net annual ET requirement for turf grass ranged from 15.65 inches in Waterloo to 73.40 inches in Phoenix, Tempe, and Scottsdale.

Daily Per Capita Use

REUWS-pie-chart

Per capita daily indoor water use was calculated for each study site and for the entire study using data logging results from 28,015 complete logged days to calculate water consumption and mail survey responses to count the number of people per household.  Across all 1,188 study homes in the 12 study sites the mean per capita indoor daily water use was 69.3 gallons (including leakage). Results are shown as a percentage pie chart above and as a bar graph below.  Toilet use was calculated at 18.5 gallons per capita per day (gpcd), clothes washer use was 15.0 gpcd, shower use was 11.6 gpcd, faucet use was 10.9 gpcd, leaks were 9.5 gpcd, baths were 1.2 gpcd, dishwasher use was 1.0 gpcd, and other domestic use was 1.6 gpcd.  Mean indoor per capita use in each study site ranged from 57.1 gpcd in Seattle, Washington to 83.5 gpcd in Eugene, Oregon.

REUWS-gpcd-chart

Leaks

In the REUWS it was found that a small number of homes were responsible for the majority of the leakage.  While the average daily leakage was 21.9 gallons, the standard deviation was 54.1 indicating a wide spread in the data.  The median leakage rate was only 4.2 gallons per household per day.  Nearly 67 percent of the study homes leaked an average of 10 gallons per day or less, but 5.5 percent of the homes leaked an average of more than 100 gallons per day.  Saying it another way, 10% of the homes logged were responsible for 58% of the leaks found.

In the 100 data logged homes with the highest average daily indoor water use, leaks accounted for 24.5 percent of average daily use.  These top 100 homes averaged 90.4 gallons per day (gpd) of leaks compared with 21.9 gpd for the entire 1,188 home data logged group.

Toilets

In the REUWS, the average measured toilet flush volume was 3.48 gallons per flush.  An average of 5.05 flushes per person per day were measured.  Only 8.5% of the homes in the study used ULF (1.6 gpf toilets) exclusively.  Another 26.2% of the study homes were found to have a mixture of ULF and non-ULF toilets.  The remaining 65.3% of the study homes did not use a ULF toilet during the study period.

Clothes Washers

Across all 1,188 logged households in the REUWS, the average loads of laundry per household per day was 0.96 (this includes the 26 logged homes which reported they did not have a clothes washer on the mail survey).  The mean daily per capita clothes washer usage across all households was 15.0 gpcd.  Clothes washers were run an average of 0.37 times per person per day and dishwashers were run an average of 0.1 times per person per day. 

The average volume per load of clothes was 40.9 gallons with a standard deviation of 12.2 and a median volume of 39.8 gallons.  Seventy-five percent of the observed loads were between 25 and 50 gallons.  The range in volumes indicates the variety of clothes washers in service which includes extra large top loading machines and low volume horizontal axis washers.  Also influencing the distribution is the tremendous number of wash settings available on modern clothes washers.  Users are often able to individually adjust the size of the load, the number of cycles, the water temperature, etc.

Showers

In the REUWS, the average shower used 17.2 gallons and had a duration of 8.2 minutes.  The average flow rate for showers in the REUWS was 2.2 gallons per minute.  Participants in the REUWS took an average of 0.75 shower and baths (combined) per person per day.