Greywater is lightly used, moderately clean wastewater that comes from domestic water sources such as bathtubs, showers and washing machines. Greywater can contain organic and inorganic contaminants such as dirt, food or mild soaps. However, it cannot come into contact with any hazardous chemicals, like those from water softeners or fecal contamination. This differentiation is important because if the wastewater comes into contact with a hazard, it can no longer be reused.
Greywater is most prominently used for irrigation purposes. Left untreated, the greywater can be used to supply water to plants that are not being grown as a food source, such as landscaping plants. The organic materials in the greywater act as a fertilizer and help provide nutrients to the plants and soil. The microorganisms and plants will filter out these nutrients and clean the water, which is naturally introduced back into the water cycle.
If the greywater is treated, it can be used to irrigate plants that produce food, but this largely relies on creating a treatment method based on the specific greywater. Besides gardening and landscaping, greywater can be used to flush toilets in a household. Many different greywater systems can be installed based on how a household wants its greywater distributed. Harnessing greywater is especially important in areas west of the Colorado River because of water scarcity in those regions.
Sources
“About Greywater Reuse.” Greywater Action, https://greywateraction.org/greywater-reuse/.
Brain, Roslynn; Lynch, Jeremy; and Kopp, Kelly, "Graywater Systems" (2015). All Current Publications. Paper 805. https://digitalcommons.usu.edu/extension_curall/805.
Everly, Jeyree. “Grey Water Uses: What Is Grey Water and What Can You Do With It?” Enviro Design Products, 25 June 2021, https://www.envirodesignproducts.com/blogs/news/grey-water-uses-what-is-grey-water-and-what-can-you-do-with-it.