How To Use Graywater

Reusing household graywater to irrigate plants, flush toilets, and wash clothes is a smart way to avoid rising water costs and preserve valuable resources.
May/June 2001
The indoor graywater-irrigated planter bed in Wellfleet Audobon Sanctuary, Wellfleet, Massachusetts, manages all of the graywater from the building’s sinks. Treated water also flows to the exterior gardens to irrigate and fertilize the plants.

When you wash your hands and then watch the water slip down the drain, do you ever wonder if there’s a less wasteful way to make use of it? Take heart! Increasing numbers of home­owners are using the water that drains from showers, tubs, and washing machines—known as “graywater”— to irrigate plants, flush toilets, and even wash clothes.

A wide variety of systems and components are available to filter, treat, and use household graywater—from ponds and aerobic planter beds to peat filters, sand filters, aerobic aquatic systems, and reverse osmosis membranes. “It’s all a matter of context,” explains Art Ludwig, author of Branched Drain Graywater Systems (Oasis Design, 2000). Because of climate, environmental conditions, costs, and laws, what works for Southern California might not work for the Northeast, Ludwig says.

Although it’s difficult to generalize, here are the basic components and guidelines for creating your own graywater system.

Choosing a system

When choosing a graywater-use system, consider these questions.

How will you use the water? Using it for growing nonedible plants requires little filtration and no disinfection. To recycle it for flushing toilets and washing clothes requires potentially costly advanced filtration and disinfection. Weigh the costs, the avoided costs, and the benefits.

What's in the water? Know what you pour down the drain. Can you avoid toxic substances such as chlorine bleach?

What do local wastewater regulations allow? Installing a graywater system may require a special permit. Call your local health agency.

What are you willing to spend? The cleaner you want your graywater, the more it may cost.

Filter it

Graywater must be filtered to remove particles and dirt that can clog pipes and soils. This is especially important for washing machines, because many modern clothes contain fibers that do not biodegrade. Filters designed to be installed at each source of graywater include thirty-micron filters, which are connected to sink and laundry drains, and grease interceptors (typically made for kitchen sinks), in which grease floats to the top and heavy solids fall to the bottom. Some systems catch and filter graywater flows with peat, sand, and other media. Higher-tech filter options include reverse osmosis systems, which push effluent through porous membranes.

All filters must be emptied out or cleaned with a backflush of water periodically. Never dispose of their contents in the sink drain.

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.”

Using graywater also requires a consciousness of what is put down the drain—toxic chemicals, drain cleaners, and strong disinfectants must be avoided.

Is it legal?

As both regulators and property owners come to accept the merits of graywater recycling, it is going public. Many graywater systems—some legal and some not so legal—have been installed in California, the first state to enact graywater regulations and promote graywater’s use during droughts. Now several others, including Massachusetts, Arizona, and Washington, are following this lead, and more will likely come on board as the laws relax and system costs decrease.

Is it foolproof?

Careful design and planning is key, or your graywater experience may go sour. Inadequate ventilation of indoor systems can lead to unpleasant odors. Using soil in a graywater system is another common mistake, Del Porto explains. Carbon from soaps, detergents, and body oils can clog the soil, making it anaerobic, foul-smelling, and ineffective. “You need air spaces for aerobic transformation and nitrogen to avoid carbon buildup that will clog the soil,” he explains. “That’s why chunky sand and other large and porous growing media are best.”

Graywater at work

Ludwig, whose small Santa Barbara home features an Eden-like variety of fruit trees irrigated with graywater, says that few of the graywater systems he designs get legal approval because of the cost and complication of meeting codes. An exception is a “branched drain system” that he designed for a neighboring home, which distributes graywater under eight inches of soil (in the root zones of plants) in a yard filled with fruit trees. Basins of mulch provide more aerobic treatment and evaporation.

In a central Massachusetts home, graywater irrigates an aerobic planter bed containing thirsty tropicals such as banana trees, birds of paradise, bamboo, and bougainvillea. The entire system is housed in a greenhouse that also helps heat the home. “The owners are thrilled,” says Del Porto, the system’s designer. “They didn’t know that such a system was possible.”

Del Porto’s firm designs systems for clients whose homes in environmentally sensitive areas require nonpol­luting wastewater solutions. Many clients learn about such systems when touring his ecologically retrofitted home near Boston. Outside the home, a bed of evergreen shrubs is irrigated by filtered graywater from Del Porto’s washing machine. Within a two-story attached solar greenhouse, graywater from some of the home’s sinks is filtered, treated in aerobic planter beds, and then drained to a fountain and pond containing koi fish and water hyacinths.

In a small atrium hallway at the Wellfleet Audubon Sanctuary in Wellfleet, Massachusetts, a twenty-foot-long planter bed brims with a dense riot of tropical greenery. This planter manages all graywater from the restroom sinks and the employee kitchen. Any overflow drains to an outdoor sand filter planted as a garden to attract butterflies.

More and more graywater-use options and installations will emerge as economy meets ecology over issues of wastewater pollution and water supply. “In the near future, a building’s landscape will also be part of its wastewater treatment system,” Del Porto predicts. “Water is getting too expensive to throw away, and wastewater is becoming even more of a water pollution problem. Increasingly, it will be strategically used up on site.”


Aquatic Eco-Systems
Apopka, FL
(407) 886-3939

Center for Ecological Pollution Prevention
Concord, MA
(978) 318-7033
Books and workshops about graywater systems

Earthship Biotecture
Taos, NM
(505) 751-0462

Jade Mountain
Boulder, CO
(800) 442-1972

Nutricycle Systems
Jefferson, MD
(301) 371-9172

Oasis Design
Santa Barbara, CA
(805) 967-9956

Sustainable Strategies
Concord, MA
(978) 369-9440

Round River Alternatives
Finland, MN
(877) 391-0888