Using Grey Water for Irrigation in the Organic Garden

Organic gardeners may cast a wistful eye at the gallons of water that disappear down the drain during the summer, when the water bill can soar into the triple digits for drought-stricken lawn and garden irrigation. Can a gardener find an easy way to recycle water for the landscape?

What is Grey Water?

Grey water includes the water used in the household from bathroom sinks, washing machines, and bathtubs. Grey water doesn’t include toilet water, or rainwater harvesting. Many states categorize the water used in dishwashers and kitchen sinks as black water rather than grey water, because of the amount of nitrogenous waste and bacteria in this water.

Is Grey Water Safe for Plants?


Gardeners may think that grey water is just as safe, if not safer, to use in the garden than rainwater from rain barrel, especially if the gardener uses natural and organic soaps and cleansers. However, most states prohibit the use of grey water that homeowners divert directly from the washing machine or shower to the garden. Why is this? Unlike freshly harvested rainwater, grey water is often contaminated with harmful bacteria, specifically fecal bacteria. This issue is a particular concern if gardeners plan to use grey water on edible crops. The presence of sodium and chloride in grey water can also damage plants.

Grey Water Systems

A grey water treatment system is more than just a holding tank. Advanced grey water recycling systems use a series of filters and settling tanks, which remove harmful bacteria that can lead to the contamination of edible crops or the pollution of adjacent waterways. Homeowners can expect to pay between $700 and $3000 for the installation of a grey water system, according to Greywater Action. Such a system can yield approximately 73,000 gallons of recycled water each year for the average household.

Recycling Household Water for the Garden

If a grey water treatment system isn’t an option for the garden, there are other ways gardeners can safely recycle household water for landscape use. The water used for cooking vegetables and eggs is excellent for watering houseplants and container plants. Gardeners should use only cooking water that doesn’t have any salt or oils added, although spices and herbs are acceptable.

A superior, but often overlooked source of recycled water is the indoor aquarium or outdoor fishpond. One of the best ways to ensure the continued health of fish in an aquarium or pond is to replace 10 percent of the water with fresh water weekly. The water one removes from the aquarium or pond is a rich source of nutrients for all garden plants. In fact, recycled aquarium water is similar to a weak form of fish emulsion, which is a coveted organic fertilizer. Gardeners can use recycled fish water to nourish seedlings and as a foliar spray in the garden.