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Decide what greywater to reuse and what to exclude

Greywater is safer than blackwater, but it still carries germs and chemicals. Choose sources and household products carefully.

How

1. Good sources: laundry, showers, baths and bathroom basins.
2. Exclude kitchen sink and dishwasher water unless your local code allows it (California excludes it).
3. Exclude water from washing nappies or soiled clothing, and water containing bleach, fabric softener, solvents, paint, oily rags or photo chemicals.
4. Use liquid detergents free of salt, sodium and boron, as salts build up in soil and harm plants.
5. Never store raw greywater for more than 24 hours (UC Cooperative Extension). It turns septic and smelly.
6. Fit a three-way diverter valve so greywater can go to the septic tank or sewer when products are unsuitable, in wet seasons or in frost.

Safety: Greywater can contain E. coli, Salmonella, Giardia and other pathogens. Avoid contact and wear gloves.

Sources

1. Use of Graywater in Urban Landscapes. University of California Cooperative Extension, accessed 2026-11
2. Laundry to Landscape Graywater System Design Guidelines. County of Santa Cruz Environmental Health, accessed 2026-11

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