Probability of Water Fixture Use during Peak Hour in Residential Buildings

The standard method for estimating instantaneous peak water use in premise plumbing systems (PPSs) is Hunter’s (1940) design curve, showing water demand versus fixture units. In recent years, federal regulations have mandated efficient water fixtures and, coincidentally, per capita water use has declined dramatically. As a consequence, Hunter’s iconic design curve no longer applies to many contemporary PPSs. In this study, high-resolution indoor water-use data from more than 1,000 single-family homes across the United States were analyzed to estimate the peak hour probability of use ($p$-values) for efficient water fixtures. Concurrent water-use profiles in different single-family households were combined to determine fixture $p$-values for multiapartment buildings. Results show that during the peak hour in single-family homes, $p$-values ranged from 0.5% to 5.5% at typical household fixtures. In a multiunit complex, the $p$-values tend to diminish as the number of units in the building increases, converging to baseline slightly lower than the single-family case. The $p$-values reported here can be used to help predict peak indoor water demand in residential buildings. These $p$-values represent current residential water-use habits and provide a first step in efforts to update Hunter’s classic method for estimating peak indoor water demand in buildings.