Peter Mayer was the lead author of this landmark study, funded in combination by the Water Research Foundation and 14 cities across the US and Canada, disaggregated water use data were obtained from nearly 1200 single family residences. In addition to characterizing water use in the single-family sector, these data were used to develop models of residential water use based on the demographic characteristics of the households and the specific water using fixtures and appliances present.
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Unveiling the Hidden Depths of Household Water Use: Insights from a Landmark Study
Ever wondered exactly where all the water goes in your home? Is it the long showers, the laundry, or perhaps something more elusive? For years, water utilities, planners, and conservation professionals faced a significant challenge: a lack of precise data on residential “end uses” of water. Most existing information was highly site-specific, making it difficult to understand national trends or effectively design conservation programmes.
Enter the Residential End Uses of Water Study (REUWS). Funded by the AWWA Research Foundation and a consortium of 22 municipalities and water providers across North America, this landmark study set out to answer these long-standing questions.
How They Did It: A Deep Dive into Water Consumption
The REUWS project team employed a multifaceted and rigorous approach to gather unparalleled data. The core of their methodology involved compact data loggers attached directly to residential water meters. These ingenious devices recorded water flow in 10-second intervals, creating detailed “flow traces”.
This high-resolution data, coupled with a custom “Trace Wizard” software, allowed analysts to disaggregate nearly two million individual water use events – from a single toilet flush to an entire clothes washer cycle – across 1,188 homes in 12 North American locations. This was a significant leap beyond previous studies, which often relied on intrusive counters or less precise methods. Complementing this, the study also gathered extensive household information through detailed mail surveys from approximately 6,000 homes and analysed historic water billing records from 12,000 residences.
Key Findings: Where Does Our Water Really Go?
The study provided invaluable insights into single-family residential water consumption:
- Indoor Water Dominates, with Toilets Leading the Way:
- The mean per capita indoor daily water use across all study homes was 69.3 gallons.
- Toilets emerged as the largest indoor water consumer, accounting for 26.7% of indoor water use.
- Clothes washers were second at 21.7%, followed by showers and baths at 16.8%.
- Faucets contributed 15.7%, and surprisingly, leaks accounted for 13.7% of indoor water use.
- The Hidden Drain: Leaks are a Major Issue:
- While average daily leakage was 21.9 gallons per household, the median was only 4.2 gallons per day, indicating that a small number of homes were responsible for the majority of leaks.
- 10% of homes accounted for 58% of all leaks. The top 100 leaking homes averaged 90.4 gallons per day in leaks.
- The study suggests that targeting homes with high winter water use (exceeding 400 gallons per day) could be an effective strategy for identifying significant leak problems.
- Conservation Effectiveness: What Works and What Needs More Study?:
- Ultra-low-flush (ULF) toilets (1.6 gpf) showed a net potential saving of 10.5 gallons per capita per day (gpcd) when compared to non-ULF homes. Importantly, the study found no evidence of “double flushing” in ULF homes, which was a common concern.
- Low-flow (LF) showerheads (2.5 gpm or less) demonstrated potential savings of 4.5 gpcd. However, homes with LF showerheads tended to take longer showers (8 minutes 30 seconds compared to 6 minutes 48 seconds in non-LF homes), partially offsetting some of the water savings.
- The study’s findings on low-water-use landscaping (Xeriscape™) were inconclusive, potentially due to self-reported data inaccuracies and the initial watering needs of new landscapes.
- Daily and Hourly Rhythms of Water Use:
- Overall residential water use follows a classic diurnal pattern: lowest at night (11 p.m. to 5 a.m.), highest in the morning (5 a.m. to 11 a.m.), moderate midday, and high in the evening (6 p.m. to 11 p.m.).
- Outdoor use typically ramps up earlier in the morning (5 a.m.) than indoor use (7 a.m.) and shows a secondary peak in the early evening.
- Predictive Models: Forecasting Future Demand:
- The REUWS successfully developed predictive models that link water use to socioeconomic factors, housing characteristics, water and sewer pricing, and climate data.
- These models are crucial tools for utilities to forecast residential water demand and assess the potential savings from various conservation measures. For instance, a one percent increase in the marginal price of water could lead to a 0.49 percent decrease in leakage. Homes with in-ground sprinkler systems used 35 percent more water outdoors, and those with automatic timers used 47 percent more.
The Way Forward: Recommendations for Future Research
This comprehensive study lays a robust foundation for understanding residential water use. However, the research team highlights several areas for future exploration:
- Targeted Conservation Retrofit Studies: Implementing a “before and after” study where homes are fitted with advanced conservation equipment would provide invaluable data on actual savings.
- Expanding Scope: Similar research is needed for multi-family residential water use and commercial and institutional sectors.
- Enhanced Data Logging: Longer and more strategically timed data logging periods could provide even greater insights into seasonal variations and their impacts on water usage patterns.
The REUWS dataset is an open resource, available for further analysis by researchers and planners, promising to deepen our understanding of this vital resource for years to come. Understanding these patterns is not just about numbers; it’s about enabling communities to make smarter, more sustainable water management decisions for everyone.
