Water Energy Nexus
Santa Fe continues to decrease its gallons per capita (that’s per person) per day water usage. As a community we are now under 100 gpcd. We can all be proud of our efforts to conserve water. However, several European countries are in the 6070 gpcd range, so obviously there is room for improvement. But how lowcan we go?
Just for fun, let’s play with some numbers and a scenario to see what is possible. Let’s use a two-person householdwith an average monthly per-person water use of 1,000 gallons and an annual rainfall of 12 inches. The house has a 1,700-squarefoot roof, a system that brings rainwater into the house for toilet-flushing and clothes-washing, and a greywater system that is plumbed to irrigate the yard.
This household would consume about 24,000 (1,000 gallons x 2 people x 12 months) gallons a year. By industry standards, slightly over 30 percent of this would be used for toilet-flushing and clothes-washing, or about 7,200 gallons a year. Assuming there is an efficient rainwater collection system, the house harvests over 12,000 gallons a year. So all the toilet-flushing and clothes-washing could be handled by the rainwater system and water savings could be subtracted from our usage figure, since these appliances would no longer be using drinkingwater.
About 30 percent of water consumed inside the house produces greywater and could be used for outdoor irrigation. Typically in arid areas, outdoor irrigation account for about 40 percent of the annual water use, or about 9,600 gallons a year. In our scenario the greywater would yield about 7,200 gallons a year. With the leftover rainwater and this greywater, it would be more than enough to handle typical irrigation needs.
The only items left in the imaginary home are drinking/cooking water, shower/bath/hand-washing water, and leaks. This is about 30 percent in a typical home based on national averages. This would be about 7,200 gallons a year. Assuming— and this is a really big assumption — that the gallons per capita per day was reduced by the same percentage above, we are now well below 50 gpcd and leading those European countries.
It is possible? Tools such as theWater Efficiency Rating Score (WERS) help builders, architects, and homeowners model different water-conserving devices. Builders such as Bob Kreger of Kreger Design Build, Santa Fe, are doing just that. “You may very realistically expect today to design and build a home that uses little to no water beyond capturing and storing rainwater, even in a semi-arid high-mesa climate like Santa Fe,” Bob said. “Performance-driven water conservation software such as WERS informs us how to offset demand of precious potable water with rain capture and storage. “
It is truly possible. We can go much lower.
Doug Pushard, founder of the website www.HarvestH2o.com, has designed and installed residential rainwater systems for over a decade. He is a member of the Santa FeWater Conservation Committee, a lifetime member of the American Rainwater Catchment Systems Association, and an EPAWaterSense Partner. He can be reached at doug@HarvestH2o.com.