An AWWA study researches the how, where and why of water use in homes.

What once was a monster of national averages, speculation and guestimation is now a complete and comprehensive study of how and where North American households use water.

The American Water Works Association Research Foundation (AWWARF) has completed its two-year study, The Residential End Uses of

Water Report, and is prepared to answer age-old questions such as: How much water is used for toilets, showers, faucets and all other purposes? What component of total use can be attributed to each specific water-using fixture? What are the factors that influence single-family, residential water use?

Survey Says É

Approximately 1 million individual water use "events" were collected from 1,188 residences. A total of 26,981 loads of laundry were recorded over the 28,015 logged days of the study. Participants took an average of 0.75 showers per person per day, and ran their faucets an average of 8 minutes per capita per day.

First discovered in the study was the difference in percentages between outdoor and indoor water use. Across all 12 study sites, 42 percent of annual water use was for indoor purposes, while outdoor was 58 percent.

In daily per capita use, indoor water use was at 69 gallons (including leakage). The water closet was calculated at using 18 gallons per capita per day (gpcd), clothes washer use was 15 gpcd and shower use was 12 gpcd. Faucet use was found at 11 gpcd with leaks right behind at 10 gpcd. At the bottom of the list were baths at 1.2 gpcd, dishwasher use at 1 gpcd and all other domestic use at 1.6 gpcd.

The study also took into account the difference water-efficient fixtures have on the percentages. For residences without water-conserving fixtures, toilets used the most water at 20 gallons per person per day (gppd). Clothes washers came next at 15 gppd and showers rounded out the top three at 13 gppd.

In residences with water-conserving fixtures (such as a 1.6 gpf toilet and 2.5 gpm showerheads), clothes washers used the most water at 15 gppd. Next came faucets at 11 gppd and showers at 10 gppd.

Knollenberg Down The Drain

Low-flow, 1.6 gpf toilets were not found to require much in the way of additional flushes to equal the performance of older, less water-efficient models, according to the study. The 1.6 gpf toilets were flushed an average of 5.04 times a day, while the larger 3.5 gpf toilets were flushed an average of 4.92 times per day. In short, the study found an insignificant difference in the flushing numbers. The study indicated that low-flow water events used 40 percent less water for flushing. This implies an average water savings of 19 gallons per household per day for retrofit groups (nearly 7 gallons per person per day).

The study also found that homes built in the 1950s and 1960s were more likely to have been retrofitted with more efficient toilets, and homes in the 1990s were already installed with efficient toilets. The study deduces from those findings that homes built in the 1970s and 1980s are better targets for retrofit and low-flow toilet rebate programs.

Household size was an important indicator of water use for toilet flushing. However, the model estimates suggest that the impact on water use for toilet flushing depends on the age groups in the household. Teens, on average, use more water than adults.

The amount of water used for toilet flushing was found to be negatively related to the number of persons employed full-time outside the home, since some flushing at home is replaced by flushing at work.

The study interpreted the number of toilets at a residence to be a surrogate for the standard of living, with results indicating that water use for toilet flushing increased with the size of the house. Also, renters were found to use 10 percent more water for toilet flushing.

Time of the year and seasonal change became factors as well. Households logged from September to November used about 12 percent more water than those who were logged in the winter.

Shower Power

The number of persons per household was also a determining factor in the amount of water used for showers and baths. Water use increased in houses with children, and teens used incrementally more water for showers than did adults. Also, shower use increased with the number of persons employed outside the home, suggesting a higher frequency of use for those preparing for work.

The study found that renters used more water for showers. Households with 2.5 gpm showerheads on average used about 9 percent less water for showers than households not completely retrofitted.

É And All The Rest

Faucet use is strongly related to household size. While the addition of small children add less to total faucet use, the addition of teens and adults increases water use. Similar to the toilet model, faucet use is negatively related to the number of persons working outside the home. Also, faucet use is lower for those who have an automatic dishwasher.

Dishwasher use was not affected by the number of teens or children in a household. However, it was negatively related to the number of residents employed full-time outside the home. And households that reported using conserving behavior (i.e., washing fuller dishwasher loads) used about 7 percent less water for dishwashing.

Clothes washer use increased incrementally with the number of teens living in the household and the number of persons working full-time outside the home. The average volume per load of clothes was 41 gallons. Of the observed loads, 75 percent were between 25 and 50 gallons. Influencing the distribution is the number of wash settings available on modern clothes washers.

Hourly Use

Using compact data loggers and a PC-based flow trace analysis software, researchers monitored the water meters of participating households for approximately four weeks. The data collection was divided into two, two-week intervals spaced to capture summer (peak) and winter (off-peak) time frames.

The start time of each water use event was stored along with the volume, duration and flow rate, so it was possible to total the volume of water used during each hour of the day. The study found the time pattern of overall residential water use followed a classic diurnal pattern in all 12 study sites with four distinct typical characteristics:

  • Lowest usage during the night (11 p.m. to 5 a.m.).

  • Highest usage in the morning (5 a.m. to 11 a.m.).

  • Moderate usage during the midday (11 a.m. to 6 p.m.).

  • High evening usage (6 p.m. to 11 p.m.).

Shower, toilet and clothes washer use all peaked during the morning "rush" to get ready for work. Dishwashers' peak time was during midday, while faucets were the only fixture to peak in the evening for cooking and cleaning.

The Low-Down On Leaks

Average daily leakage was 22 gallons, with higher leakage registered for households logged during the winter months. The quantity of water leaks showed a relationship with both the marginal price for water and the marginal price for sewer. The study findings seem to verify that higher prices lead to a degree of voluntary leak detection and correction. Renters had lower amounts of leakage than non-renters. The study attributes this to landlords seeking to minimize costs.

Also, the amount of leaks was shown to increase with the number of toilets in a home. Houses built in the 1970s were found to have higher leakage.

The Study's Approach

Twelve study sites (14 cities) volunteered to participate in the study and partially fund the research. In addition to the household monitoring, 12,000 households had their historic billing records incorporated into the survey. Also, household level information on 6,000 households was obtained through a detailed mail survey.

The study sites included: Boulder and Denver, Colo.; Eugene, Ore.; Seattle, Wash.; San Diego and Lompoc, Calif.; Phoenix, Tempe and Scottsdale, Ariz.; Tampa, Fla.; the Regional Municipality of Waterloo, Ontario; Walnut Valley Water District, Calif.; and Las Virgenes Municipal Water District, Calif.

While the study sites did not statistically represent all North American locations, there was a diversity of water use data found over the 12 locations, which suggests that the data has "transfer" value across North America.

The results of the study did not simply create national water use averages; this was the first comprehensive study of water end use to include socioeconomic and casual factors, and finally make the information useful to the trade.

Copies of the AWWARF Residential End Uses of Water Study will be available in December. Call 800/926-7337 to order by phone. Additional information on the End Uses study can be found on PM's Web site