Greywater: What is it?

Greywater is wastewater from:

• bathtubs,

• showers,

• bathroom sinks,

• washing machines,

• dishwashers and kitchen sinks,

• any source in your home other than toilets.

Greywater can be used in place of fresh water to irrigate (below ground) the roots of trees, shrubs, and flowers.

It's important to understand that greywater can contain harmful bacteria, viruses, and chemicals that pose a risk to public health and the environment if mishandled.

What's in Greywater?

Source: Adapted from Small Flows Quarterly, Winter 2001, Volume 2, Number 1

Why Conserve Water?

Conserving our water resources is important in times of normal rainfall, but even more so during periods of extended drought. Our ground water and surface water supplies can be emptied faster than they can be refilled with rain and snowmelt. By using water wisely now, you help to ensure that there will be enough water for everyone in the future.

If handled carefully, greywater can be used in place of fresh water in subsurface irrigation systems. However, using less water in the first place is cheaper, easier, and safer than installing a greywater system for irrigating your landscape, and it's something everyone can do!

Water Conservation Tips:

• Install low-flow water fixtures and water efficient appliances.

• Repair leaky plumbing fixtures.

• Take shorter showers.

• Choose landscaping that does not require large amounts of water.

• Water landscapes before 10 AM or after 7 PM.

Benefits of Using Greywater

• Use less fresh water.

• Possibly save money by using less fresh water.

Disadvantages and Cautions with Greywater

• Handle greywater carefully because it can contain bacteria and viruses.

• Do not drink greywater or apply it to anything that may be eaten.

• Do not use greywater to irrigate food root crops such as carrots or potatoes, etc. Fruit trees are OK if irrigated below the surface at the roots.

• Do not water lawns with greywater using a sprinkler.

• Do not use greywater to wash patios, walkways, or driveways.

• Greywater collection, storage, and subsurface irrigation systems are usually cheaper and easier to install during construction of a new home. Re-plumbing an existing building can be expensive and may be impractical.

• Greywater may not meet all of your landscape irrigation needs all year round. Some times of the year, your plants may need more water than can be supplied by your greywater irrigation. Other times of the year, your home may generate more greywater than your plants can use.

• Some chemicals in greywater can be harmful to plants.  (See information about plants that may be suitable for greywater).

• Grease and oils can cause problems with distribution piping, so be careful to manage what goes down the drain!

• Greywater irrigation must not be used above ground. It needs to be 6 inches or more below the surface.

• If separating greywater from black water is a problem, you might want to consider using a Subsurface Drip System (a type of septic treatment system).

Handle Greywater Safely

DO NOT drink greywater or apply it on anything that may be eaten, including root crops such as potatoes or carrots.

DO NOT water lawns with greywater using a sprinkler, or use greywater to wash patios, walkways or driveways.

Did You Know.......?

• Greywater makes up the largest portion of wastewater from your home; up to 40 gallons per person each day.

• Greywater systems must irrigate below the ground surface by using a drainfield or a suitable drip irrigation system to reduce health risks.

• Greywater systems are usually cheaper and easier to install during construction of a new home. Re-plumbing an existing building can be expensive and may be impractical. If separating greywater from black water is a problem, you might want to consider using a Subsurface Drip System (a type of septic treatment system).

• Subsurface irrigation with greywater offers a way to conserve water. However, greywater may not meet all of your landscape irrigation needs all year round. Subsurface irrigation with greywater is different from Onsite Subsurface Drip Systems.

• Some chemicals in greywater can be harmful to plants. For example, liquid detergents generally have less sodium than powdered detergents and are recommended when irrigating with greywater.  For more information about using greywater for subsurface irrigation, see the Recommended Standards and Guidance . . . for Water Conserving On-Site Wastewater Treatment Systems.

How do I safely install and use a subsurface greywater irrigation system?

Contact your county health agency for:

• wastewater treatment system permits (greywater is wastewater),

• design requirements,

• a list of qualified designers and installers.

Develop a design that matches your specific needs and options for greywater use. The design of the system will depend on:

• the source and characteristics of the greywater,

• the physical characteristics of the site,

• a landscape design taking into consideration the kinds of plants and how tolerant they may be to greywater,

• local code requirements,

• how, when, and where the greywater will be used.

Apply greywater safely:

• irrigate with greywater 6" below the surface of the ground,

• irrigate ornamental landscapes such as shrubs, trees, and flowers,

• regularly check your greywater system to be sure it is functioning properly.

Plant Choices for Greywater

Some times of the year, your plants may need more water than can be supplied by greywater irrigation. At other times of the year, your home may generate more greywater than your plants can use.

Some chemicals in, and characteristics of, greywater can be harmful to plants. For example, some studies have shown that greywater from kitchens that have dishwashers can be quite damaging to plants because of the very high pH (i.e. pH of 10). Few, if any, plants will survive very high pH.

For more detailed information, see the Recommended Standards and Guidance . . . for Water Conserving On-Site Wastewater Treatment Systems.

Why Purple for the Greywater Subsurface Irrigation Emitter Pipes?

For outdoor applications, if the greywater is delivered to a conventional drainfield there are no special color requirements.

But if the greywater is used for subsurface irrigation, the emitters must be colored purple to identify the non-potable water source.

More Resources on Greywater:

• Water conservation and drought information is available at the Washington State Department of Health Office of Drinking Water website.

• For information about on-site wastewater treatment systems (septic systems), please visit the Washington State Department of Health, Wastewater Management Section web page.

Telephone: (360) 236-3062
E-mail:  WastewaterMgmt@doh.wa.gov

• The National Small Flows Clearinghouse provides information on small community and individual on-site sewage systems.

• If separating greywater from black water is a problem, you might want to consider using a Subsurface Drip System.