WHAT IS GRAY WATER?

"Gray water" is wastewater collected from clothes washers, bathtubs, showers, and laundry or bathroom sinks. If properly collected and stored, it can be safely re-used, thereby reducing fresh water consumption. Reuse of gray water can also reduce the load on septic tanks and leach fields.

Gray water is distinguished from "black water", which is wastewater from toilets, kitchen sinks and dishwashers. Black water should never be reused in the home because of possible contamination by bacteria, viruses, and other pathogens.

Gray water may contain food particles, detergent or soap residue, and possibly some human pathogens. But as a general rule, gray water does not require extensive chemical or biological treatment before being used for landscape irrigation. Gray water can be put to other uses. It is best to use gray water on ornamental plants and lawns, or to irrigate trees, rather than on food plants, especially those that are often eaten raw; such as carrots or lettuce or herbs.

Soap and detergent are the components in gray water, which could adversely affect plants the most. The wastewater from the shower or lavatory sink generally contains only a small amount of soap, and has few solid residues. However, re-using water from a clothes washer may be much easier, from a plumbing standpoint. Special detergents can be purchased to lessen any harmful impacts on plants.

Gray water may be immediately directed to landscaping, or it may be stored for later use. When stored, filtering the water is more important, to reduce the growth of any pathogens. Gray water should not be used for dust control, cooling, spray irrigation, or any other use that would result in air-borne droplets or mist.

CAUTION: In some areas, reuse of water is either prohibited by health officers and/or plumbing inspectors, or requires an inspection and permit. Make sure that it is legal in your area before setting up a gray water collection site in your home!

Re-use of gray water in Arizona used to require a permit, which could be granted only after the homeowner submitted specific design plans for review. The plans had to meet stringent chlorination, sampling and filtering requirements, which were so onerous and expensive that essentially no one applied for the permits. Yet, studies showed that tens of thousands of homeowners were reusing gray water anyway, and that the health risks associated with gray water were not that serious, and could be greatly reduced if some simple guidelines were followed.

As a result, the State of Arizona's Department of Environmental Quality in January 2001 instituted a general permit for homeowners whose gray water systems meet the following Best Management Practices:

• First and foremost, avoid human contact with gray water.
  
  
• You may use gray water for household gardening, composting, and lawn and landscape irrigation, but it should not run off your property.
  
  
• Do not surface irrigate any plants that produce food, except for citrus and nut trees.
  
  
• Use only flood or drip irrigation to water lawns and landscaping. Spraying gray water is prohibited.
  
  
• When determining the location for your gray water irrigation, remember that it cannot be in a wash or drainage way.
  
  
• Gray water may only be used in locations where groundwater is at least five feet below the surface.
  
  
• Label pipes carrying gray water under pressure if confusion between gray water and drinking water pipes is possible.
  
  
• Cover, seal and secure storage tanks to restrict access by small rodents and to control disease-carrying insects.
  
  
• Hazardous chemicals, such as antifreeze, mothballs and solvents, cannot be in gray water. Do not include wash water from greasy or oily rags in your gray water.
  
  
• Gray water from washing diapers or other infectious garments must be discharged to a residential sewer or other wastewater facility, or it can be disinfected prior to its use.
  
  
• Surface accumulation of gray water must be kept to a minimum.
  
  
• Should a backup occur, gray water must be disposed into your normal wastewater drain system. To avoid such a backup, consider using a filtration system to reduce plugging and extend the system's lifetime.
  
  
• If you have a septic or other on-site wastewater disposal system, your gray water use does not change that system=s design requirements.

If not otherwise prohibited in your area, gray water systems constructed and operated according to these Best Management Practices are likely to provide you with a safe method of reducing your water demand.

If you produce less than 400 gallons of gray water a day, you don't need a permit for recycling gray water. Older houses generate about 46 gallons of gray water per day per household member; new construction generates 35 gallons per person per day. Even if you don't need a permit, state regulations require that you:

• Have a house that isn't in a flood plain.
  
  
• Use gray water from only your residence for irrigation only on your property.
  
  
• Do not use the water for irrigation of food plants, except citrus and nut trees.
  
  
• Connect your gray water system to a septic or sewer system in case it has problems.
  
  
• Have a secure cover for gray water storage for mosquito control and safety.

Some Do's and Don'ts About Graywater

Do:

1. Filter your gray water with something as simple as a stocking to trap hair and lint.

2. Frequently check your plants for evidence of overwatering or damage from organic material in gray water.

3. Use gray water only for flood or drip irrigation.

4. Divert gray water to your sewer or septic system if you are laundering diapers or dyeing clothes.

5. Structure your irrigation system so it doesn't waste water by letting it percolate beyond the root zone.

6. Use PVC or ABS piping.

Don't:

1. Drink your gray water!

2. Reuse water that contains hazardous chemicals from photo labs, car parts or oily rags.

3. Allow your gray water to pond because it can increase health risks and provide breeding grounds for mosquitoes.

4. Reuse gray water for spray irrigation.

5. Irrigate root or leaf crops (such as carrots or lettuce) that you'll eat.

6. Reuse gray water if family members suffer from infectious diseases, such as diarrhea, hepatitis or internal parasites.

SOURCE: Arizona Department of Environmental Quality,
1-800-234-5677