What is Greywater?
Greywater is wastewater from bathtubs, showers, bathroom sinks, washing machines, dishwashers, and kitchen sinks - any source other than toilets and urinals.
Chapter 246-274 WAC sets requirements for using greywater for subsurface irrigation. The rule took effect on July 31, 2011. Local health jurisdictions (LHJs) have three years to implement it. (LHJs may adopt more stringent requirements than those in the state rule.) However, if they are unable to adjust resources to implement and enforce this chapter, the provisions of chapter 246-272A WAC shall continue to apply to greywater reuse for subsurface irrigation. Check with your LHJ to learn if greywater reuse under chapter 246-274 WAC is allowed or ask them how to support that effort if it is not allowed yet.
Did You Know...?
Greywater makes up the largest portion of wastewater from your home...up to 40 gallons per person each day.
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.
Subsurface irrigation with greywater offers a way to conserve water. However, greywater may not meet all of your landscape irrigation needs all year round.
Greywater systems must irrigate below the ground surface by using a drainfield or a suitable drip irrigation system to reduce health risks.
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. See Irrigating Plants with Greywater for more information.
What's Harmful About Greywater?
Greywater can contain chemicals, bacteria, viruses, and other pollutants that, if mishandled, can pose a risk to public health and the environment. The amount of pollutants carried by greywater varies depending on what goes down the drain. When people manage what goes down the drain, the amount of chemicals and pathogens can be reduced significantly.
Greywater reuse is one option for reusing wastewater. There are many other options for conserving water and recycling wastewater. To learn more about the available options in the state of Washington, go to our Water Conservation and Water Recycling webpage.
The new rule requires that the design and management of a subsurface greywater irrigation system be based mainly on the source and volume of the greywater. The amount of greywater that can be applied must not be more than what can be absorbed by plants and lost to evaporation. Greywater used for subsurface irrigation can only be applied during the growing season.
Greywater from bathroom/lavatory basins (sinks), showers, tubs, and clothes washing machines have relatively low levels of pathogens, chemicals, and fats, oil, and grease. Flows from these sources are defined as light greywater.
Greywater from non-laundry utility sinks and the kitchen, including sinks and dishwashers, typically contain more pathogens, chemicals, and fats, oil, and grease. Flows from these sources are defined as dark greywater.
The following table lists some of the characteristics of different sources of greywater:
Bacteria, bleach, foam, high pH, hot water, nitrates, oil and grease, salts, soaps, suspended solids.
Bacteria, hair, hot water, odor, oil and grease, soaps, suspended solids.
Bacteria, food particles, hot water, odor, oil and grease, soaps, high pH and sodium (from dishwasher), suspended solids.
Adapted from Small Flows quarterly newsletter, Winter 2001
Design and Management
System design and management requirements depend mainly on greywater source and volume.
Local rules may be more restrictive than state rules. Check with your local health jurisdiction before planning a greywater reuse system.
The state rule uses a risk based approach for greywater reuse to protect public health and the environment. The following table defines the three "tiers" that determine the type of system required:
|Source of Greywater
|Treatment and Distribution
|Less than 60 gallons per day per irrigation system - limit 2 per building
|No treatment - gravity
(Exception: Treatment is required when used in a public location such as a playground, school, church, or park)
|Less than 24 hours per day
|Less than 3,500 gallons per day
|No treatment - even distribution (typically by pressure)
|Less than 3,500 gallons per day
|Treatment Required - even distribution (typically by pressure)
*To learn about tier two and tier three systems read Guidance for Performance, Application, Design, and Operation & Maintenance of Tier Two and Three Greywater Subsurface Irrigation Systems (PDF).
Tier one systems are simple systems that use gravity to distribute light greywater, a surge or storage tank may not be used. The cost of installing one is less expensive than a tier two or three system, however, gravity distribution systems are not capable of distributing the greywater as evenly or precisely as pressure systems. To maximize water recycling, a tier two system is preferred.
The Tier One Greywater System Checklist and Irrigation Area Estimation Tool (PDF) provides more information about using tier one systems. Check with your local health jurisdiction to find out if tier one greywater systems are allowed in your county. Your county may have a specific Greywater System Checklist for you to use.
To learn more about greywater reuse go to our Useful Greywater Links webpage.
A tier two greywater irrigation system uses a surge tank, storage tanks, or pump(s) and stores light greywater for less than 24 hours.
A tier three system requires an approved treatment component to treat dark greywater, light greywater stored for longer than 24 hours, light greywater to be used to irrigate a green roof, or any greywater used in a public location such as a playground, school, church, or sports field.
The use of a greywater irrigation system does not serve as an alternative to an approved on-site sewage system or connection to an approved public sewer. Greywater irrigation systems designed and installed under Chapter 246-274 WAC are intended for temporary, seasonal use. Diversion valves that redirect greywater to the permanent sewage treatment system are required on all greywater irrigation systems.