Reference
Using Greywater in the Garden Safely
The short answer
Greywater, the gently used water from showers, baths, bathroom sinks, and laundry, can be reused in the garden, but Extension sources set firm safety limits. The central rule is that it should not be used on edible plants: keep greywater off root crops entirely, and make sure the edible parts of any plant never contact it. Ornamentals, lawns, and non-food trees are the safe targets; fruit trees can be irrigated only if the water is applied to the soil and doesn't splash the fruit.
Beyond what you water, three rules matter. Use plant-friendly soaps and detergents, avoiding products with sodium, boron/borax, chlorine bleach, or heavy salts, which build up in soil and harm plants. Apply greywater below the soil surface via drip or subsurface lines rather than a sprinkler, so you avoid aerosols and skin contact, and never store it more than 24 hours because it turns foul fast. Finally, legality varies widely by state and locality, so check the rules and permit requirements where you live before setting up a system.
Never on the food you eat
This is the non-negotiable rule. UC Master Gardeners state plainly: do not use greywater on edible plants, including root crops or edible parts of any plant, and do not eat any plant or fruit that has been in contact with greywater on the plant surface or in the soil. Root crops like carrots, radishes, potatoes, and onions are off-limits because the edible part grows in the very soil the greywater wets. Fruit trees and berry bushes can be irrigated, but only if the water goes to the soil and does not splash the fruit. Arizona's guidance similarly restricts greywater away from food crops as a health precaution.
⚠ Greywater is not sterile: it carries traces of soap, food particles, skin, and potential pathogens. Keeping it away from the parts of plants you eat is the core safety principle.
Choose the right soaps
- Avoid detergents with sodium or salts, which accumulate in soil and make it hard for plants to take up water and nutrients.
- Avoid boron, borax, and borate, which are toxic to plants even at low levels.
- Avoid chlorine bleach, and products with dyes, whiteners, fabric softeners, and heavy fragrances.
- Favor liquid, low-sodium, plant-safe soaps; bar soaps and powdered detergents tend to be higher in salts.
How to apply it, and check the law
Deliver greywater to the soil, not through the air. UC guidance is to avoid sprinkler systems, which create aerosols that can carry microbes, and to use subsurface or drip delivery instead, distributing the water evenly rather than pooling it in one spot. Do not store greywater more than 24 hours, since its organic load quickly consumes oxygen and turns smelly. Legality varies by jurisdiction: some simple laundry-to-landscape systems are exempt from permits, but altering household plumbing or adding pumps and tanks often triggers permit requirements, and states like Arizona and Colorado have their own rules. Confirm local regulations before building anything. For everyday watering, see our water and irrigation guides.
Sources
Reviewed 2026-07-18. We cite university Extension, government, and established horticultural sources — and never invent pesticide rates or dangerous treatments.
- UC Master Gardeners of San Luis Obispo County - Graywater Irrigation — Do not use graywater on edible plants including root crops or edible parts; do not eat plants or fruit contacted by graywater; avoid soaps with borax, salts, sodium, chlorine; do not store graywater over 24 hours; do not use in sprinkler systems; permits may be required if plumbing is altered.
- University of Arizona Cooperative Extension - Using Gray Water for Irrigation — Greywater should be stored no more than 24 hours and should not be used on food crops (Arizona restricts food-plant use, with limited exceptions such as citrus/nut trees where fruit is not splashed); apply below the surface and avoid sprinklers.