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The Homeowners Column
Going Green May Mean Going Grey - Using greywater in the landscape
State Master Gardener Coordinator
Too much rain there: not enough rain here. Water is a crucial commodity, often in short supply this time of year. Lately 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 that I just enjoyed a shower. I feel like the villainous cowboy in an old western. As the bad guy forces the good guys to trudge across the desert, he drinks the last drop of water from the canteen while the parched good guys watch their last hope for water evaporate.
All that slightly used household water we watch go down the drain is called greywater. It includes 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.
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.
- Only use greywater on ornamentals. Do not use greywater on edible crops especially root crops such as carrots which may be eaten uncooked.
- Use compost and mulch around plants to help decompose contaminants and to hold in moisture.
- 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 greywater per square foot of soil.
- Do not use greywater in the 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 particularly small containers.
In 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 not set up to easily recover greywater. For us it usually means a bucket brigade. I use a dish pan to collect my rinse water from dish washing. If you decide to change your home plumbing to allow access to greywater, 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 or a friendly plant.