Almost exactly half of residential water use consists of water used outside the home (e.g., for watering lawns), according to a recent NAHB study. Indoors, the biggest users of water are toilets, followed by showers, faucets, clothes washers and leaks.
These results of the NAHB are based on data that became available in 2016 in the form of Residential End Uses of Water (REUW), a detailed study and data set of single-family homes produced by the Water Research Foundation.
In total, the single-family homes in the REUW study used an average of 276 gallons of water per day (gpd). Almost exactly half of this was attributable to water used outside the home. It is well known that lawns and gardens need more watering in climates that are hot and get little natural rainfall, so this helps explain the climate-related pattern to state water use per housing unit shown in last week’s post. Indoors, toilets account for the greatest share of water use, but the shares for showers, faucets, clothes washers and leaks are also substantial.
The numbers in the chart above include both hot and cold water. The water heater in and of itself is not counted as an end use; the end use is where the water goes after leaving the heater. If storing water in a tank to heat it increases indoor water use, this would not be characterized as an identifiable end use and would show up in the “other” category. The 2016 REUW studies hot water use specifically in a sample of 94 homes and found that hot water accounted for one-third of total indoor water use.
Although it is not feasible to parse specific indoor uses by age of structure in the REUW data, it is possible to do this for total water used per single-family home. Results show less water used by homes built before 1960, but relatively small differences among homes built after that. For example, there is less than a 3 percent difference between the 244 gpd used by homes built in the 1960s and the 251 gpd used by homes built after 1999.
One possible explanation for lower water use in homes built before 1960 is the incidence of swimming pools. Not surprisingly, statistical models in the REUW study indicate that swimming pools have a particularly strong impact on household water use. Although 12 to 15 percent of homes built after 1959 in the REUW data have swimming pools, swimming pools are present on only 8 percent of homes built in the 1950s and only 3 percent of homes built before 1950.
This result, along with many others, is discussed more thoroughly in the full NAHB study.