Greywater is wastewater from household sources excluding toilets: bathroom sinks, showers, bathtubs, washing machines, and laundry sinks. Greywater contains lower levels of pathogens and organic matter than blackwater (toilet waste) and can be recycled for landscape Irrigation. A well-designed greywater system diverts 50 to 80 percent of household wastewater to irrigation, reducing water consumption and the load on septic or municipal treatment systems.
Greywater reuse has been practiced informally for centuries, with household wash water being used to water gardens. Modern greywater systems were developed in the 1970s and 1980s in response to drought and water scarcity concerns. The state of California adopted the first greywater standards in the 1990s, and many states now permit greywater systems under specific regulations.
The simplest and most widely approved greywater system is the laundry-to-landscape (L2L) system. The washing machine discharge hose is connected to a diverter valve that directs water to a 2.5 centimeter (1 inch) irrigation line. The water flows through a series of 1.3 centimeter (0.5 inch) drip tubes to mulched basins around trees, shrubs, and ornamentals. No filtration is required because the washing machine's lint filter removes solids. Biodegradable, low-sodium laundry products are used to prevent soil and plant damage.
A constructed wetland treats greywater through biological and physical processes in a lined, planted basin. Water flows through a gravel bed planted with wetland species such as cattails, rushes, and sedges. Microorganisms on the plant roots and gravel surfaces break down organic matter, and plants absorb nutrients. The treated water can be used for subsurface irrigation of fruit trees and ornamental plants. Constructed wetlands require a larger area than L2L systems but provide higher treatment levels.
Greywater regulations vary by jurisdiction. Most states permit simple laundry-to-landscape systems without a permit. Systems that include bathroom sinks and showers typically require a permit and may require subsurface irrigation only. The International Plumbing Code includes provisions for greywater systems. Local health departments should be consulted before installation.