Greywater & Rainwater Catchment

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Greywater is water from showers, bath tubs, washing machines, and bathroom sinks. It is water that contains some soap and detergents, but is clean enough to water plants. You can use greywater for landscape irrigation through the use of mulch basins or drip irrigation fields to irrigate ornamental plants or trees in your yard. Greywater can be applied to the subsurface or may be released at the ground surface if at least two inches of mulch, rock, soil, or a solid shield covers the release point. Ponding or surface runoff is prohibited and greywater must be contained on the site where it is generated. Greywater can be stored for up to 24 hours. After 24 hours it is considered black water and must be disposed in sewer or septic. A permit is not required for a laundry to landscape system. Greywater systems collecting water from sources other than a clothes washer or those connected to the plumbing system do require permits. Please contact the Town's Building Department for information on Town permits and the County's website for information on County permits:

Links to Additional Greywater Resources:


Rainwater Catchment

Rainwater and stormwater, captured and properly managed, can contribute significantly to local water supplies by infiltrating and recharging groundwater aquifers, thereby increasing available supplies of drinking water. In addition, the onsite capture, storage, and use of rainwater for nonpotable uses significantly reduces demand for potable water, contributing to the statutory objective of a 20% reduction in urban per capita water use in California by December 31, 2020.

Anyone can capture rainwater no matter what size of property you have (Portola Valley has no specific prohibitions against rainwater capture, but depending on how it is done, other Town regulations may apply).  Catchment surfaces can be virtually any impervious surface. There are a variety of solutions.  As examples:

  • Small lots: rain barrels, rock sumps and weirs in rain gardens
  • Medium lots: above ground cisterns, straw wattles, rain gardens, dry streambeds and sand filters
  • Large lots: large underground storage tanks/cisterns, swales, weirs, retention ponds, wetlands and terraces

In the short-term rainwater capture can be used for irrigation. The real value lies in the long term: capturing rainwater for rebuilding our watersheds and replenishing the aquifer. Slow it; Sink it; Save it.


Links to Additional Rainwater Catchment Information: