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Sanitation · Greywater reuse and natural treatment · sanitation-16Size the greywater irrigation area
The irrigation area must absorb all greywater without ponding. Use your greywater volume and soil type to size it.
How
- Estimate greywater per day from the flow calculator, or use the California method: 15 US gallons (about 57 L) per occupant per day for laundry, counting 2 occupants for the first bedroom and 1 for each extra bedroom.
- Find your soil type from the soil evaluation.
- Use the greywater irrigation calculator, which applies the California Plumbing Code table (for example 40 sq ft per 100 gallons a day in sandy loam).
- Spread outlets so each area gets no more than the soil can absorb in a day.
- Increase the area in wet climates and on slopes, and check that no water runs off your land.
Sources
- Laundry to Landscape Graywater System Design Guidelines. County of Santa Cruz Environmental Health, accessed 2026-11