Greywater

What is greywater

Greywater = wastewater from showers, tubs, bathroom sinks, and laundry (not toilets). Typically 50-80% of household wastewater volume. Mildly contaminated with soap, hair, lint, body oils, food particles. Decomposes naturally and quickly under aerobic conditions.

Blackwater = toilet wastewater. Substantially more contaminated; requires more treatment.

Kitchen sink = often categorized as “dark grey” or treated as blackwater because of food particles, grease, and pathogens.

System types

Laundry-to-landscape (L2L):

• Washing machine drain hose redirected to outdoor irrigation system
• No alterations to plumbing
• No permits required in most U.S. states
• Cheapest and simplest greywater system; moves ~10-25 gallons per load directly to fruit trees, shrubs, or large garden plants

Branched drain (gravity-fed):

• Bathroom sinks, showers, tubs drain to a network of gradually-stepped distribution lines
• Each line ends in a mulch basin around a fruit tree or large plant
• No pumps; gravity-driven; minimal maintenance
• Permits often required; codes vary

Pumped greywater systems:

• Greywater collected in surge tank, pumped through drip irrigation
• More distribution flexibility but more components and maintenance
• More likely to require permits

Indoor-reuse systems:

• Greywater treated (filtration, UV, sometimes biological) and reused for toilet flushing
• More complex; more regulated; more useful in arid urban contexts

Compatible plants

Greywater works well for:

• Fruit trees (apple, pear, citrus, fig, [[pomegranate|pomegranate]])
• Shrubs ([[rosemary|rosemary]], [[lavender|lavender]], currants, ornamentals)
• Most vegetable crops where water reaches the root zone, not edible parts directly
• Lawns (less efficiently)

Avoid greywater for:

• Plants where edible parts touch [[soil|the soil]] (leafy greens, root vegetables) without proper soil-contact buffering
• Plants sensitive to soap (some seedlings)
• Acid-loving plants (greywater often slightly alkaline from soap)

Considerations

• Soap matters — biodegradable, low-sodium, low-boron soaps; avoid bleach, fabric softener, harsh chemicals
• Mulch basins — distribute water under mulch; aerobic decomposition; no standing water
• Don’t store greywater — use within 24 hours; standing greywater becomes blackwater
• Permits — vary widely; check local codes; many U.S. states have streamlined greywater codes since the 2010s

See also

Auto-generated from this entry’s typed relations: frontmatter, grouped by relation type so the editorial signal isn’t flattened.

• Shares approach with: [[rainwater-harvesting]] · [[water-cycle]]
• Member of: [[practice]]

Sources

• The Water-Wise Home, Laura Allen (Storey, 2015)
• Create an Oasis with Greywater, Art Ludwig (Oasis Design, multiple editions)
• Greywater Action (greywateraction.org)

Rooted in life.