Throughout the United States, periodic droughts can leave water in short supply. Reusing and recycling water helps decrease demand and ensure more water is available for everyone. Water can be recycled at an individual level by homeowners, or at a municipal or county level through nonpotable and indirect potable reuse.
Greywater is household wastewater from bathroom sinks, showers, tubs and washing machines; it has not come into contact with feces or passed through a toilet (see References 1 and 2). Some intrepid homeowners recycle their greywater by using it to water their lawns or gardens or by using it to flush their toilets (see References 1). The greywater can be treated first, or it may be used untreated; under no circumstances, however, should it contain bleaches, dyes, bath salts, fabric softeners or detergents containing boron — an excess of boron is toxic to plants (see References 1 and 2). Note that different states have different regulations governing greywater reuse — check with local authorities for details.
Tips for Greywater Recycling
If you plan to recycle your greywater, it's essential to ensure that nothing potentially corrosive or toxic to your plants goes down your drain (see References 1 and 2). If the water you use to wash dishes is untreated, it may contain grease and fats, so it's not suitable for use as greywater. Greywater with excess salt is also potentially damaging to plants. If you are using your greywater to flush your toilet, pump or discharge it into the toilet bowl — do not feed it directly into the toilet tank, which could cause a blockage. Treating your greywater increases the cost of the system but may avoid some of these issues. A settling tank or septic tank can help remove many kinds of contaminants, and the addition of an aerator can increase the oxygen content of the water. Filters and chlorination are other options (see References 1).
Municipalities treat sewage before releasing it into the environment. Primary treatment removes solid objects, grit, oils and grease; sewage that has passed through primary treatment only is unfit for reuse. Secondary and tertiary treatments use an aeration basin, where microbes consume organic waste, followed by clarification, disinfection and filtering (see References 3 and 4). Water from a secondary treatment process can be used to irrigate nonfood crops or for industrial cooling, while water from a tertiary treatment process can be used for landscape and golf course irrigation, crop watering or toilet flushing. This kind of water is called nonpotable, because it's not intended for human consumption; consequently, this recycled water must be kept separate from the city water supply (see References 3).
Indirect Potable Reuse
Some cities and counties have turned instead to indirect potable reuse, where wastewater is purified to exceed drinking water quality standards and then added to reservoirs or aquifers to indirectly augment the potable water supply (see References 5 and 6). In Orange County, for example, the Groundwater Replenishment System uses wastewater to produce up to 70 million gallons of potable water per day, as of 2011. The end product is pumped into injection wells and recharge basins, where it eventually reenters Orange County's groundwater supply (see References 5).
- New Mexico State University; Safe Use of Household Greywater; Marsha Duttle; February 1994
- Greywater Action: About Greywater Reuse
- U.S. Environmental Protection Agency: Water Recycling and Reuse: The Environmental Benefits
- "Essential Environment: The Science Behind the Stories, 2nd Edition"; Jay Withgott and Scott Brennan; Prentice Hall; 2007
- Groundwater Replenishment System: Purification Steps
- City of San Diego; Indirect Potable Reuse Opportunities; March 2006
Based in San Diego, John Brennan has been writing about science and the environment since 2006. His articles have appeared in "Plenty," "San Diego Reader," "Santa Barbara Independent" and "East Bay Monthly." Brennan holds a Bachelor of Science in biology from the University of California, San Diego.
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