The Homeowners Column

The Homeowners Column

Using Greywater in the Landscape

Photo of Sandra Mason

Sandra Mason
Extension Educator, Horticulture
slmason@illinois.edu

You won't find any vacation brochures about greywater rafting. There isn't any level 5 greywater. Greywater is not nearly that exciting because it's waste water from showers, bathtubs, dishwashers, washing machines and sinks. It's basically any household water other than toilet water. About 65% of domestic wastewater is greywater. That can translate into as much as 40 gallons per person per day. For a family of 4 that's about 5,000 gallons of greywater a month which just about fills a backyard swimming pool.

What is in the greywater varies with its source, but may include bacteria, foam, hair, grease, soaps, detergents, oils and food particles. Sounds gross I know, but many times the water is quite clean. Just think of how many gallons we use just waiting to get that perfect temperature for our showers.

With this drought I've been thinking a lot about water and all the fresh water or just slightly "used" water that goes down the drain. I look at my thirsty plants and I feel guilty. Lately I feel like the bad guy in all those desert movies. You know the one that drinks the last drop of water from the canteen while the thirsty good guys melt into their clothes. While greywater doesn't need extensive treatment before it can be used for landscape watering, some precautions should be kept in mind.

  • Apply greywater directly to soil not onto plants. Subsurface application is even better.
  • Use greywater within 24 hours of collecting it. Do not store it for long periods.
  • Avoid using greywater on edible crops especially root crops such as carrots which may be eaten uncooked. Even better, use greywater only on ornamentals.
  • Use compost and mulch to help decompose contaminants.
  • Do not use greywater on acid loving plants such as rhododendrons and blueberries. Greywater tends to be alkaline.
  • Disperse greywater over a large area and rotate with fresh water to avoid buildup of sodium salts. One recommendation from the University of Massachusetts is to apply no more than one half gallon of grey water per square foot of soil.
  • Do not put greywater into toilet tank.
  • Use garden friendly soaps. Most hand and dish soaps and shampoos will not damage plants at low concentrations. Laundry detergents should be free of sodium, boron, borax, chlorine and phosphates. Liquid detergents are generally better than powdered. Avoid laundry soaps with bleaches or softeners.
  • Washing machine greywater should not be used if laundry includes diapers or oily rags.
  • With greywater from the kitchen sink, avoid using the water if you have washed a lot of greasy pans or if the water contains a lot of food particles.
  • Do not use water from automatic dishwashers. It tends to have more sodium, bleach and borax and has a very high pH that can harm plants.
  • Use on established plants, not on new transplants.
  • Do not use on indoor plants or outdoor plants in small containers.

In more arid regions of the U.S. some people have their plumbing systems set up to reuse greywater for irrigating the landscape. Our plumbing systems are just not set up that way. Recovering greywater for reuse is not as easy for us. For us it usually means a bucket brigade. I use a dish pan to collect my rinse water. If you decide to change your home plumbing to allow access to grey water, check with your local health department and a licensed plumber before making any changes. We take fresh water for granted so save water and shower with a friend.

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