Single-family homes built after the 1990s have an average of 3.1 toilets, 2.6 showers and 2.3 bathtubs, according to a recent NAHB study.
Standard tables from the Survey of Construction (SOC, conducted by the U.S. Census Bureau with partial funding from HUD) show that the share of single-family homes built with at least 2 bathrooms has increased regularly from 60 percent of homes completed in 1973 to 97 percent of homes completed in 2016.  This suggests that the number of bathroom fixtures should also be on the riese, but this is not one of the things that it has been possible to investigate using SOC data.
It can be investigated, however, with data that has recently become available from the Residential End Uses of Water (REUW) study from the Water Research Foundation (WRF).  The REUW is the source of information on water use in single-family homes in the recent NAHB article on the topic.  Consistent with the increasing number bathrooms, the REUW data show that the average number of toilets, showers and bathtubs all increase regularly as single-family homes become newer. For example, the average number of toilets increases regularly from 1.9 in homes built before 1960 to 3.1 for homes built after 1999.
Perhaps surprisingly, the published REUW study did not show a statistical relationship between the number of bathroom fixtures and the amount of water used by a particular single-family. The WRF constructed several models from REUW data, estimating outdoor water use, total indoor use, and a number of different individual indoor uses. NAHB economists reviewed these models and judged them to be generally well constructed and a good use of the available data, and saw no obvious reason to critique them or suggest alternatives.
Although the number of bathroom fixtures does not affect water use in any of the WRF models, the presence of efficient toilets and clothes washers does. Given government standards that have been promulgated and modified since 1990, it should not be surprising that efficient fixtures were most common in the newest REUW homes. For example, of the homes built after 1999, 71 percent had toilets that averaged less than 1.6 gallon per flush, 51 percent had toilets that averaged less than 1.28 gallons per flush and 80 percent had ENERGY STAR rated clothes driers. All three of these percentages are higher than they are for homes in any of the earlier vintage categories
Estimates of total water use, as well as the amount of water used by specific features, in single-family homes were discussed in last week’s post. For a more thorough discussion of the REUW and what if finds has an impact on water used by a single-family home, please consult the full NAHB study.
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