For a typical single-family home, plumbing fixtures may account for what fraction of the home’s total indoor water use?

According to foundational data from the U.S. Environmental Protection Agency (EPA) WaterSense program, which informs the LEED rating systems, the primary indoor plumbing fixtures are the largest water consumers in a typical home. Toilets account for approximately 24%, showers for 20%, and faucets for 19% of indoor water use. The sum of these fixtures is 63%, which is most closely approximated by the fraction 2/3 (66.7%). The LEED for Homes rating system heavily focuses its Water Efficiency (WE) credits on reducing water use from these specific fixtures due to their significant collective impact on total consumption.

A. 1/3: This fraction (33.3%) significantly underrepresents the combined water use of toilets, showers, and faucets, which are the three largest end uses.
B. 1/2: This fraction (50%) is too low, as it fails to capture the full impact of the three main fixture categories in a typical, non-high-efficiency home.
D. 3/4: This fraction (75%) overestimates the contribution from fixtures by not adequately accounting for other major uses like clothes washers (~17%) and leaks (~12%). ---

1. U.S. Environmental Protection Agency (EPA). "Indoor Water Use in the United States." WaterSense Program. This foundational document provides the widely cited pie chart breaking down residential indoor water use, where toilets, showers, and faucets sum to over 60%. (See "Sources of Indoor Water Use" graphic).

2. U.S. Green Building Council. LEED v4.1 Residential Design and Construction Reference Guide. Washington, D.C.: USGBC, 2021. The introduction to the Water Efficiency (WE) category and the rationale for Prerequisite WE "Indoor Water Use" are based on the premise that fixtures are the dominant indoor water users, justifying the focus on fixture efficiency standards.

3. DeOreo, W. B., Mayer, P. W., et al. Residential End Uses of Water, Version 2: Executive Report. Water Research Foundation, 2016. This peer-reviewed study provides detailed end-use data for single-family homes, confirming that toilets, faucets, and showers are the largest components of indoor water consumption. (See Table ES-1, Summary of Average Daily per Capita Indoor Water Use).