Residential Water Use Summary

from AWWARF Residential End Uses of Water study

Copyright 1999 Aquacraft, Inc. and American Water Works Association Research Foundation. All rights reserved. Reproduction without permission is prohibited.

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Mean daily per capita water use, 12 study sites

Leaks

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.

Clothes Washers

A total of 26,981 loads of laundry were recorded over the 28,015 logged days during the study. Across all 1,188 logged households in the REUWS, the average loads of laundry 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.

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.

Fixture Utilization

The data collection technique employed in the REUWS made it possible to calculate mean daily fixture usage for toilets, showers, clothes washers, dishwashers, baths, faucets, etc. Study participants across all 12 study sites flushed the toilet an average of 5.05 times per person per day. The participants took an average of 0.75 showers and baths combined per person per day. 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. Faucet utilization was calculated in terms of minutes per capita per day rather than as a count of faucet uses per day. Study residents ran their faucets an average of 8.1 minutes per capita per day.

ULF Toilet Savings

Of the over 289,000 toilet flushes recorded during the two year end use monitoring, 14.5 percent of the flushes were less than 2.0 gpf, 34.7 percent of the flushes were between 2 and 3.5 gpf, and 50.8 percent were greater than 4 gpf.

Of the 1188 data logged homes, 101 (8.5 percent) used ULF toilets almost exclusively. This number was determined by first calculating the average flush volume for each study residence. Homes with an average volume per flush of less than 2.0 gallons over the 4 week data logging period were classified as "ULF only" homes meaning that while they may have other units, they use ULF units almost exclusively. The 101 "ULF only" homes used an average of 24.1 gallons per household per day (gpd) for toilet purposes. The residents of these homes flushed the toilet an average of 5.04 times per person per day and used an average of 9.5 gpcd for toilet purposes.

Another 311 study homes (26.2 percent) were found to have a mixture of ULF and non-ULF toilets. These homes were distinguished by counting the number of toilet flushes which used less than 2.0 gallons per flush. Homes that had six or more ULF flushes (and who were not part of the "ULF only" group were placed in the "mixed" toilet group. Homes with a mixture of ULF and non-ULF toilets used an average of 45.4 gpd for toilet purposes. The residents of these homes flushed the toilet an average of 5.39 times per person per day and used an average of 17.6 gpcd for toilet purposes.

The remaining 776 study homes we placed in the "non-ULF" group. The "non-ULF" study homes averaged 47.9 gpd for toilets. Residents in these homes flushed an average of 4.92 times per person per day and used an average of 20.1 gpcd. The net potential savings when comparing "ULF only" homes from this study to the "non-ULF" homes is therefore is 10.5 gpcd.

LF Shower Savings

So called "Low Flow" shower heads are designed to restrict flow to a rate of 2.5 gpm or less. By calculating the modal shower flow rate for each shower at each study residence it was possible to separate homes which always showered in the low-flow range (LF houses), homes which occasionally showered in the low flow range (Mixed houses), or homes which showered exclusively above the low flow range (Non-LF houses). About 15 percent of the study homes showered in the low flow range exclusively, 60.4 percent occasionally showered in the low flow range, and 24.5 percent showered exclusively above the low flow range.

The LF shower homes used an average of 20.7 gpd and 8.8 gpcd for showering, while the non-LF shower homes used an average of 34.8 gpd and 13.3 gpcd. However, the duration of the average shower in the LF shower homes was 8 minutes and 30 seconds, 1 minute and 48 seconds longer than the average shower duration in the non-LF homes which was 6 minutes and 48 seconds.

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Copyright © 1999 Aquacraft, Inc. and American Water Works Association Research Foundation. All rights reserved. Reproduction without permission is prohibited.