Mimic the Beavers

Capturing & storing rainwater and gray water

Using her own North Park home as an elaborate test site, architect Candace Vanderhoff is on a mission to get San Diegans to “mimic the beavers” by building systems that trap water, let it sink into the soil and capture some for later use. With a few simple tools, salvaged materials, lots of mulch and a few large barrels, she can show you how to not only save water and money, but how to help heal the planet as well.

Vanderhoff, a proponent of simple, renewable living in urban areas, follows a philosophy called permaculture – working with, rather than against nature – to create self-sustaining environments. She is currently focused on conserving potable water by substituting rainwater and gray water (wastewater from sinks, showers and laundry) to transform traditional yards into regenerative, natural habitats. Her company, RainThanks & Greywater, specializes in water capture and reuse and also designs and installs edible and drought tolerant landscapes.

Gray Water Systems

At a workshop held at CCSE in September, Vanderhoff explained that the average California family of four uses about 400-600 gallons of water a day, half of that for irrigation and nearly one-third for showers and laundry. By reusing that one-third that now goes into sewers for irrigation, it would greatly reduce the total used. Vanderhoff points out that about 90 percent of the county’s water is imported from the Colorado River and Northern California.

Thanks to the drought in California in 2009, the state eased regulations for recycling residential wastewater, making it legal to use gray water from bathroom sinks, showers and laundry for irrigation without extensive underground systems and, in some cases, without a permit. In other states, residents have been recycling gray water for years.

Key California gray water provisions:

Single water sources, such as a clothes washer, do not require a permit.
Gray water must be covered by mulch if discharged above ground to stop run-off or pooling.
No gray water should be discharged below three feet above groundwater level.
All gray water systems must be equipped with a valve that allows water to be routed into a sewer system if necessary.
No gray water is to be used on or near root crops.

According to Vanderhoff, a successful home gray water system meets three basic requirements:

Site considerations – Is there sufficient space to construct the necessary mulch pits? Does the slope keep the gray water on the property?
Plumbing access – Can you get to pipes and drain lines to install new gray water lines? Are pipe heights and slopes adequate to keep flow moving outside and to the mulch pit?
Soil infiltration – At what rate does the water percolate into the soil? The California gray water code provides an infiltration requirement based on soil type, with very clayey soil needing 1.1 square foot per gallon of gray water per day and sandy soil requiring about 0.2 square foot per gallon per day.

Rainwater Harvesting

Collecting rainwater is another way to decrease the amount of imported water used on trees, shrubs and lawns. While the average rainfall in San Diego is officially about 10-11 inches (measured at Lindberg Field), most of the county receives more, primarily during January through March. It doesn’t take much rain to fill a collector – one inch of rain on a 1,000-square-foot roof can yield around 600 gallons of usable water.

Rainwater is easily diverted from gutters and downspouts into barrels above ground or tanks buried in the yard. Many above ground collectors are ornamental so that they provide decoration as well. A basic rainwater barrel, with the appropriate diverters and hoses, can be set up for about $50.

Another rainwater strategy is to keep it on your property by channeling runoff into a swale (a slight depression or ditch) that is underlain with mulch, compost or riprap to facilitate infiltration into the soil.

CCSE’s Advice and Technical Assistance Center for Urban Forestry sponsored Vanderhoff’s lecture. For future urban forestry workshops, click here.

Continue reading October's newsletter.