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Build branched drain and mulch basin systems

A branched drain splits gravity-fed greywater from showers and basins into several outlets, each into a mulch basin around a tree or shrub.

How

1. Plan a continuous downhill fall from the fixture to every outlet, as this system has no pump.
2. Dig each mulch basin deep enough for water to fall freely into it and so roots do not clog the outlet.
3. Size basins to hold all the greywater with no ponding or runoff. Clay soils need larger basins than sandy soils.
4. Fill with coarse woody mulch, putting woody material near the bottom. Large wood chips last longer than fine shredded mulch.
5. Water perennial ornamentals or fruit trees. Do not apply greywater to edible parts of plants, root crops, lawns or groundcover, and do not use sprinklers.
6. Top up mulch as it breaks down and dig out basins if they start to pond.

Sources

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

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