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July 24, 2012

EcoPlanners: Water Recycling Basics Part 1: Reusing Graywater

by Claudia Harmon Worthen, EcoPlanners LLC

Graywater (Greywater, Gray Water) is simply untreated water that comes from the bath, shower, bathroom sink and washing machine or building waste water. It is non-potable water, but safe for surface (or 16″-20″ below the surface) irrigation of non-edible plants or subterranean recharging of the aquifer. “Treated” graywater can be used in SLO County, to flush toilets and urinals.

Not all laundry water may be reused. If you’ve been washing dirty diapers or other unsanitary things, the water becomes “blackwater”.  Blackwater is flushed toilet water, water from the kitchen sink, garbage disposal and dishwasher because of the high concentrations of organic waste like chicken skin and body waste.  With sophisticated treatment and filtration, blackwater can be purified to be drinkable. However, most people are don’t like the thought of reusing water that was initially so unsanitary.

Using Graywater when possible is good because it conserves potable water. The nitrogen or phosphorus found in detergents (and graywater) are good for some plants, while others find it distasteful. It is best to talk to an expert to determine if the sodium and chloride contained in some detergents are harmful to your more sensitive plants. To be safe, detergents used in the high efficiency front load washers work best for the garden.

Graywater use will lower utility bills for home &/or business and reduce stress on septic systems. If used properly, Graywater can make your garden greener and healthier. Plus, it just feels good reusing water and preserving valuable resources.

The amount of graywater produced depends on the size of a household and their water consumption.  A percentage of a household’s interior use represents supply, and its interior and exterior applications generally represent demand.  Approximately 50 to 65 percent of water applied to interior uses potentially can be recycled as graywater. The total water budget for exterior uses depends upon the type of landscaping, type of soil and the season of the year. Those of us who have gotten rid of our lawns in order to save water can once again have large expanses of guilt free green with a graywater system.

Graywater systems are divided into 4 categories: clothes washer system, simple system, complex, and treated graywater.  These systems range from rather crudely running a house from washer to your geraniums to rather complex and costly engineered systems with pumps and filters. Properly installed washer systems can reduce household landscape water use to zero.

Redirecting the washing machine to a leach field in the garden does not require a permit.  Re-directing other household fixtures for irrigation or indoor use, must be permitted.  The SLO County website contains the regulations and process under the 2007 California Plumbing Code guidelines.

Interested in learning more about using recycled water? Next week, I’ll be discussing rainwater catchment systems, another eco-friendly way to reuse water in your own home and garden.

For further information on gray water systems check out or SLO building department website at or contact [email protected]

All SLO city and county building departments and  SLO Green Build office have copies of SLO guide to the Use of Graywater.


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