How To Use Graywater
(Page 2 of 4)
May/June 2001
By Carol Steinfeld
All filters must be emptied out or cleaned with a backflush of water periodically. Never dispose of their contents in the sink drain.
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Treat it
If graywater is going to be used for flushing toilets or washing, its nutrients, bacteria, and carbon must be treated so it meets water treatment standards. One option is to run graywater through an aerobic planter bed that contains chunky growing media such as sharp sand, peastone, or gravel (even broken glass). The growing media and the plant roots provide spaces for air-using beneficial bacteria to destroy potential pathogens and convert the nutrients to a form that plants can use. These systems usually contain phreatophytes—thirsty broad-leafed tropical plants—and other fast-growing plants such as bamboo and reeds that use up the water and nutrients. (Because graywater contains few nutrients, the plants may need to be fertilized.) The plants are periodically harvested and composted or discarded.
Disinfect it
If the recycled graywater is to be used for anything that involves direct contact with people, such as flushing toilets, washing clothes, or watering edible plants, it must be disinfected. This is best done with ozone or ultraviolet light devices rather than chlorine, which is potentially carcinogenic.
Graywater use made simple
Keep a container near the sink to catch warm-up water and rinse water for watering plants. Place a bucket in the shower to collect warm-up water and shower water. Use it to flush the toilet by pouring a gallon or two into the bowl. Or use it to water your plants or compost pile.
Is it safe?
Graywater typically contains oil and grease from soaps and skin, as well as dirt, cleaning solvents, and pathogens (disease-causing organisms) from washed bodies and clothes. But separating graywater from blackwater (the effluent discharged from toilets and, under some state laws, kitchen sinks) keeps most of the potentially harmful pathogens out of graywater.
“Graywater usually has some fecal coliform in it, so it does have to be treated,” says David Del Porto of Sustainable Strategies, an engineering firm in Concord, Massachusetts. “Graywater is also high in carbon, can be alkaline, and can have lots of nonbiodegradeable particles from clothing, so it needs to be filtered.”