Several types of systems use graywater efficiently.
1. Shallow gravel or sand trenches: After filtering graywater in a surge tank, drain it into 18-inch-deep, gravel-filled trenches planted with water-loving species. This California-approved solution is relatively easy to permit in many other states.
2. Sand filter: Drained from a surge tank, graywater can be filtered through a basin full of sand before it’s piped to drip-irrigate an orchard or a greenhouse vegetable garden. In winter, divert graywater to a below-ground leachfield to avoid freezing.
3. Constructed wetlands: Wet basins full of gravel planted with water-loving species such as elephant ear and papyrus can function as a treatment system before you apply graywater to gardens. Plants and roots should be removed periodically to clear the basin of carbon residue.
4. Drip irrigation: Dispersing graywater to an entire lawn via drip irrigation—usually small hoses or pipes perforated with holes—requires filtering and treatment to avoid clogging.
5. Branched drain system and other mulch-filter systems: Graywater can be dispersed underground via a system of pipes that branch out to holes filled with woodchips, which compost the carbon and particles. In rustic variations of this, perforated basins of woodchips and straw at the outflow pipe are used to filter graywater before it’s discharged to the landscape.
6. Surface drip and spray irrigation: Spraying or otherwise applying graywater above ground usually requires, by law, disinfection through either ultraviolet or ozone disinfection or a reverse-osmosis filter. This must be approved in all states except New Mexico and Arizona.