All About Greywater Recycling and Re-use
Last updated July 20, 2009
What is greywater? It is any water that has been used within the household and ends up going down the drain, excluding toilet water or water containing high levels of organic wastes such as from the dishwasher, garbage disposal or kitchen sink. This primarily includes water from your baths and showers, bathroom sink, and clothes washing. Greywater is of lesser quality than the potable water directly from your faucet, but of higher quality than black water, hence the appropriateness of the term graywater or greywater. In the average household, approximately 50-80% of residential "waste" water is greywater that can be effectively reused for other purposes, such as watering the landscape.
What are the benefits of re-cycling greywater? If greywater is used on vegetation, fresh or potable water use is reduced, resulting in lower water costs. Not only does its use on landscape conserve potable water, but greywater actually may be healthier for some plants, resulting in more vigorous vegetation growth. Greywater may contain detergents with nitrogen or phosphorus which are plant nutrients. However, it may also contain possibly harmful chemicals sodium and chloride which sensitive plant species may not be able to safely be exposed to, thus homeowners need to use special detergents that don't contain salt or boron, compounds which dehydrate plants.
Additional benefits of greywater recycling:
- Less energy and chemical use. By re-using the greywater, less energy is needed to both deliver fresh water or treat wastewater. Fewer chemicals are sent down the drain, instead nourish the yard and plants.
- Reduced strain on septic system or treatment plant. Reusing greywater will extend the life and capacity of septic systems, while placing less burden on the community water treatment plant as well.
- Recharges groundwater. Any excess of greywater beyond vegetation needs that is added to the soil will help to recharge groundwater.
How do I select the type of greywater system to use? The first step is to assess the potential amount of greywater your home and appliances might generate. The appliance-water use listing below (source: www.graywater.com) can help you estimate usage in gallons.
- Top loading domestic washing machine: 30 gallons per cycle
- Front-loading style washing machine: 10 gallons per cycle
- Bathroom sink usage: 1 - 5 gallons average use
- Dishwasher: 3 - 5 gallons per cycle
- Low-flow showerhead: 3 - 7 gallons per shower average
The next step after you have determined the amount of greywater that you may expect your home to generate is to research the local city or government regulations regarding greywater system usage or placement. Unfortunately, not all states have "permit free" systems. In Arizona, for instance, the permit free system allows a resident to use gray water as long as they follow a set of guidelines to ensure safety and no cross contamination. Other codes, such as the state of California, are prohibitively expensive. California's code states that a legal gray water system needs to be nine inches under the ground, which may cost a homeowner up to $5000.
The next step is selecting the type of greywater system that will best fit the needs of your home. Greywater recycling systems are commercially available, and vary from simple low-cost systems to more costly complex systems. The more sophisticated greywater systems treat greywater prior to disposal to reduce groundwater contamination and surface ponding problems. Some of these systems are able to remove pollutants and bacteria from greywater. The better systems include settling tanks and sand filters. Improvement in technologies and systems' innovations regularly occur. For a reference which has some specific designs that may suite your needs, here is a link to use Oasis Designs™ guidelines for selecting your system. Many other free or low-cost sources are available on the internet to help you either design your own system or purchase one commercially, simply do an online search.
Here are some links to websites where you can learn more about greywater recycling:
A bunch of information greywater and rainwater harvesting by Brad Lancaster: http://www.harvestingrainwater.com/greywater-harvesting/
Arizona Department of Environmental Quality's Guide to Using Gray Water at Home: http://www.azdeq.gov/environ/water/permits/download/graybro.pdf
University of Arizona water resources research center: http://ag.arizona.edu/AZWATER/arroyo/071rain.html
Oasis Design, a website on all aspects of greywater systems -- why to use them, how to choose, build and use them, regulations, studies, and examples: http://oasisdesign.net/