New Public Health rules allow rainwater as sole source for residential drinking water

July 21, 2011

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The King County Board of Health today approved an environmental sustainability measure that opens new opportunities for the use of rainwater captured from roofs as the sole residential water source.

Boardmember Kathy Lambert proposed the addition of rainwater catchment systems as an additional tool to potable water sources. The proposal was in response to requests from constituents who want to build sustainable homes that reduce their impact on the environment as much as possible, and are at hardship of obtaining other water options

“Extending public water lines or digging a well are not always available or feasible in rural and rugged areas of King County, or they can be so expensive to install that they render a lot unbuildable,” said Lambert. “The ability to utilize rainwater will be a particular advantage in mountainous areas of the county with terrain and soil conditions that make it difficult to site a well and on-site sewage system that do not interfere with each other.”

The code change follows recent action by the Washington Department of Ecology to remove permit requirements for rainwater harvesting. Since last year, Public Health rules have allowed use of rainwater for drinking, but only as a secondary source in addition to public water, a well or a spring source. Today’s action allows homes with septic systems to rely only on rainwater for all uses, under certain conditions.

The new regulation requires specific roof materials and qualifications for designers of rainwater catchment systems, and also requires the systems to include filtration and disinfection systems. Cisterns would need to accommodate enough storage volume to last through dry summer months.

“An important advantage of rainwater catchment is to prevent depletion of groundwater supplies essential for adequate streamflows in low rainfall months,” Lambert said. “Harvesting rainwater also prevents stormwater runoff from roofs that otherwise would carry surface water and pollutants into watershed streams and rivers, contributing to flooding and water quality degradation.”


“Roof-top rainwater collection systems could be good solution for homeowners who want to maximize water conservation,” said Larry Fay, Manager of Community Environmental Health at Public Health - Seattle & King County. “These systems require close attention to water use management, so they aren’t right for everybody, but I'm pleased it's now an option for single family homeowners.”

“Use of rainwater as the sole source for household water encourages conservation every day, and conservation is the way we will be able to meet the water demands of the future,” said Lambert.