Residential End Uses of Water Study (2016, 1999)

water research foundation logoThe Residential End Uses of Water, Version 2 is the 2016 companion to the classic 1999 end use study published by the Water Research Foundation.  These studies carefully examined where water is used in single-family homes are the largest end use studies of their kind conducted in North America.  The “end uses” of water include all the places where water is used in a single-family home such as toilets, showers, clothes washers, faucets, lawn watering, etc.  The official results of the Residential End Uses of Water, Version 2 are available from the Water Research Foundation (WRF).

Residential End Uses of Water, Version 2 – 4309 (2016)
http://www.waterrf.org/Pages/Projects-Q.aspx?PID=4309
This project serves as a comprehensive update to WRF’s 1999 Residential End Uses of Water study. This update includes more varied site locations, hot water end use data, more detailed landscape analysis, and expanded water rates analysis. This project focused solely on single-family residences.  

Research Summary

Where is water used in single-family residences?  What is the volume of water that is used for toilets, showers, clothes washers, faucets, dishwashers, and all other purposes?  Does water use vary across single-family homes and across different cities and regions?  What factors influence single-family residential water use?  What is the impact of more efficient fixtures on residential demands?  The Residential End Uses of Water studies (REU1999 and REU2019) attempted to answer these and other questions about residential water consumption patterns.

Findings

 

Annual Use

REU2016

Average annual water use, based on historic billing records from approximately 1,000 accounts in each of the 9 study sites, ranged from 55,000 gallons per household per year in Waterloo and Cambridge, Ontario to 175,000 gallons per household per year in Scottsdale, Arizona.  Across all study sites 73 percent of annual water use was for indoor purposes and 23 percent for outdoor purposes.  This mix of indoor and outdoor was strongly influenced by annual weather patterns.

REU1999

Average annual water use, based on historic billing records from approximately 1,000 accounts in each of the 12 study sites, ranged from 69,900 gallons per household per year in Waterloo and Cambridge, Ontario to 301,100 gallons per household per year in Las Virgenes MWD.  Across all study sites 42 percent of annual water use was for indoor purposes and 58 percent for outdoor purposes.  This mix of indoor and outdoor was strongly influenced by annual weather patterns and, as expected, sites in hot climates like Phoenix and Tempe and Scottsdale had a higher percentage of outdoor use (59 – 67 percent) while sites in cooler, wetter  climates like Seattle and Tampa and Waterloo had much lower percentages of outdoor use (22 – 38 percent).  The net annual ET requirement for turf grass ranged from 15.65 inches in Waterloo to 73.40 inches in Phoenix, Tempe, and Scottsdale.

Daily Indoor Per Capita Use

The indoor per capita pie chart from the REU2016 is shown below. Toilet flushing was the largest indoor use of water per person on average (14.2 gpcd, 24%) followed by showers (11.1 gpcd, 19%), kitchen and bathroom faucets (11.1 gpcd, 19%), clothes washers (9.6 gpcd, 16%), leaks ( 7.9 gpcd, 14%), other/miscellaneous (2.5 gpcd, 4%), bathtub (1.5, gpcd, 3%) and dishwashers (0.7, gpcd, 1%).

 
GPCD-pie-REUWS-2
 

Indoor per capita daily indoor water use for each end use was calculated for the REU1999 and REU2016.  Results are shown in the figure below.  In cases where the whiskers do not overlap (toilet, clothes washer, and dishwasher), there is a statistically significant difference at a 95% confidence level.

 GPCD---REUWS-2 

Leaks

In the REU1999 and REU2016 it was found that a small number of homes were responsible for the majority of the leakage.  Leakage was reduced by 16.1% from 9.5 gpcd (REU1999) to 7.9 gpcd (REU2016), but because of the high variability in this category, this change was not found to be statistically significant.  

Toilets

Toilet use fell by 23.2% from 18.5 gpcd (REU1999) to 14.2 gpcd (REU2016).  Dishwasher use fell by 29.6% from 1.0 gpcd (REU1999) to 0.7 gpcd (REU2016).

Clothes Washers

The biggest reduction in per capita water use between the two studies was measured in the clothes washer category, which fell by 35.9%, from 15.0 gpcd in REU1999 to 9.6 gpcd in REU2016. 
 

Other End Uses

Per capita shower use was reduced by 4.3% from 11.6 gpcd (REU1999) to 11.1 gpcd (REU2016), but the change was not statistically significant.

In three categories, per capita water use increased between the two studies, but none of these increases was statistically significant at the 95% confidence level. Faucet use was almost unchanged, and increased by just 1.8% from 10.9 gpcd (REU1999) to 11.1 gpcd (REU2016). Miscellaneous/other water use (evaporative cooling, humidification, water softening, and other uncategorized indoor uses) increased by 54.8% from 1.6 gpcd (REU1999) to 2.5 gpcd (REU2016). The bathtub category increased by 20.6% from 1.2 gpcd (REU1999) to 1.5 gpcd (REU2016).