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Graywater

Colorado’s Water Plan (CWCB, 2015) predicts that Colorado will be faced with a significant water supply shortfall within the next few decades and describes strategies to eliminate the shortfall by 2030.  One strategy that the plan identifies is reuse of graywater.  When used for drip irrigation of non-food plants and for flushing toilets, graywater can help save Colorado’s limited water supplies.

Graywater is wastewater that originates from a clothes washer, bathtub, shower, or bathroom sink and can be used in your home for certain types of irrigation or for flushing toilets.  Graywater is different from “black water,” which is wastewater from toilets, kitchen sinks and dishwashers.  Black water is not safe for reuse in the home because of the high risk of contamination by bacteria, viruses and other pathogens.

Graywater sources include water discharged from:

  • Bathroom and laundry-room sinks.
  • Bathtubs.
  • Showers.
  • Laundry machines.

Graywater does not include water discharged from:

  • Toilets.
  • Urinals.
  • Kitchen sinks.
  • Dishwashers.
  • Non-laundry utility sinks.

Every time we shower or wash clothes, we make graywater that is usually disposed of. Residents can lower their water bills and conserve a valuable resource by making their systems compatible with graywater reuse. Graywater can perform two important, water-intensive functions: landscape irrigation and toilet flushing. A study by Greywater Action on residential graywater systems found that the average household saved over 14,000 gallons of water per year by installing graywater filtration systems in their homes without negatively affecting soil or plant health.

You can learn more about graywater and graywater systems at Graywater Central at Oasis.com or at Graywater Action.  Note that some of the uses and systems described on these web pages are not allowed in Colorado.  Detailed information on allowable graywater systems in Colorado can be found on the State of Colorado’s Graywater web page

Full design requirements for Denver: Rules and Regulations Governing Graywater Treatment Works

Visit Development Services’ web page for information on obtaining permits for installation of a graywater system.

A laundry to landscape graywater system is a simple system that distributes greywater from a laundry machine to multiple plants or a mulch basin. Laundry to landscape systems are relatively inexpensive and easy to install. The laundry machine’s internal pump pressurizes the greywater, so this system can irrigate plants across a flat yard.  

Laundry to landscape graywater graphic 

Laundry-to-landscape system. Image credit: CleanWaterComponents

If you are thinking about installing a laundry to landsacpe graywater system, you must comply with the following requirements:

Allowed Uses and Systems

  • Sub-surface irrigation for watering lawns or landscaping is the only allowable use of graywater generated by laundry to landscape systems.
  • Use of graywater to irrigate any plants that produce food is prohibited.  Graywater has the potential to transport disease.
  • Allowable systems include drip irrigation or designed "Mulch Basins". 
  • Systems which spray graywater are prohibited.

General Requirements

  • Avoid contact with graywater, or soil irrigated with graywater.  Graywater contains pathogens that can make you ill.
  • You may use graywater for landscape irrigation, but use it in a way that it does not pool or run off your property.
  • Don’t store graywater for more than 24 hours.  If you do, the nutrients in it will start to break down, creating bad odors.
  • Graywater cannot contain hazardous chemicals such as antifreeze, mothballs and solvents.  Do not include wash water from greasy or oily rags in your graywater.
  • Graywater from washing diapers or other infectious garments must be discharged to the sanitary sewer.

Siting Requirements

  • When determining the location for graywater irrigation, remember that it cannot be in a flood plain or a flood zone.
  • Graywater may only be used in locations where groundwater is at least five feet below the surface.

Design Requirements

  • Detailed design requirements can be found in Denver’s Rules and Regulations Governing Graywater Treatment Works.
  • Laundry to landscape graywater systems are required to have a valve that allows for diversion of graywater to the sanitary sewer when needed.
  • All pipes carrying graywater must be clearly labeled. Labelling eliminates confusion between graywater, drinking water, and wastewater pipes.
  • Cover, seal and secure storage tanks to restrict access and control disease carrying rodents and insects, such as mosquitoes.
  • Use of a filter is required to reduce plugging and to extend the system’s lifetime. Should a backup occur, graywater must be disposed into your normal wastewater system. 
  • If you have an onsite wastewater treatment system or other on-site wastewater disposal system, your graywater use does not change that system’s design requirements for capacity and reserve areas.

 

If you plan to use graywater from a laundry to landscape system for irrigation, you should be aware that laundry detergents may contain chemicals that can be harmful to your soil and plants. Here are some things you can do to help improve graywater quality and ensure your soil and plants remain healthy and hardy:

  • Use a liquid detergent. Liquid detergents contain fewer salts than powdered detergents. Salts can be harmful to plants.
  • Bypass your water softener. Water softeners add sodium which can reduce soil’s ability to absorb water.
  • Use biodegradable detergents and detergents without boron. At low levels, boron can give plant leaves a burnt appearance and at higher levels can be toxic.
  • Divert wash water from laundry loads containing high amounts of fecal matter (such as diapers) to the sanitary sewer. Fecal matter may contain disease-causing microorganisms.
  • Avoid using wash water with chlorine based bleach for irrigation. Chlorine based bleach can damage plant foliage. If you must use bleach, use a non-chlorine bleach such as hydrogen peroxide.
  • Avoid using products that contain antimicrobial compounds.
  • Avoid contact with graywater. Graywater may contain bacteria and disease-causing microorganisms that can make you or your pet sick.
  • Graywater should not be used when outdoor temperatures are below freezing, soils are frozen or when it is raining. Divert graywater to the sanitary sewer at these times to avoid damaging your graywater system and / or releasing graywater to the environment.

References

Colorado Graywater. Laundry to Landscape Best Management Practices. 1 page.

University of California Vegetable Research and Information Center. Using Household Waste Water on Plants. Universitry of California, Division of Agricultural Sciences, Leaflet, 2968, 2 pages. Available at: http://vric.ucdavis.edu/pdf/fertilization_Householdwastewater.pdf

Committee on the Beneficial Use of Graywater and Stormwater (2016). Using Graywater and Stormwater to Enhance Local Water Supplies: An Assessment of Risks, Costs, and Benefits. Water Science and Technology Board; Division on Earth and Life Studies; National Academies of Sciences, Engineering, and Medicine. The National Academies Press, 224 pages. Available at: http://www.nap.edu/21866

For more information on Graywater, its potential uses and installing graywater systems, contact the following City & County of Denver departments:

Denver Department of Environmental Health, Environmental Quality Division

720-865-5452

EQComments@denvergov.org

Department of Community Planning and Development, Neighborhood and Inspection Services Division

720-865-2705