Gray Water

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Gray Water Sample Drawing

Gray Water Sample Drawing
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GRAY WATER reuse is a much debated topic in the Public Health sector today. Generally citizens are interested in reusing water and many homes are currently being fitted with gray water recycle storage tanks. Much of this is being done by individual homeowners without jurisdictional approval. They want to conserve laundry water, bath water, rain water, etc. The problem is unanticipated contamination which can render the storage tank a health hazard and a festering, stinking mess.

The reuse of household gray water can be dangerous if improperly collected or if potable water is cross contaminated, which is exactly why Public Health Officials are having a tough time dealing with what seems to be such a good idea to the general public.

Darco manufactures underground water storage tanks that can be used for gray water storage.

Our advice at Darco:

  • Always talk with your City or County Dept. of Public Health before moving ahead.
  • Do your homework to understand the concept and possible sanitation problems.
  • Isolate black water (sewage) into a separate dedicated piping system.
  • Install a selector valve routing gray water either to storage or sewer / septic tank.
  • Install a check valve to prevent sewage backflow into the gray water system.
  • Avoid contamination from food scraps, human waste, and body fluids.
  • Don't store gray water for extended periods of time (over the winter).
  • Use gray water only for outside irrigation rather than household tasks.
  • Wear rubber gloves while watering with a hose and avoid skin contact.
  • Dilute collected household gray water with rain water if available.
  • Chlorinate the tank when full to 25 ppm for 24 hours, at least once a year.
  • Remember, if the stored water starts to smell foul, it isn't gray water anymore.

A few typical "common sense" guidelines:

  • Be sure your family knows and follows the "Household Gray Water Rules".
  • The safest gray water sources are the laundry machine and bath tubs or showers.
  • Detergents do not necessarily improve the water quality in gray water storage system.
  • When you have house guests who may not understand or follow the rules, turn your selector valve to "sewer position" to bypass potential contamination. (See Illustration #1)
  • Use caution collecting water from the kitchen sink or dishwasher as food scraps and grease will decompose over time and contaminate the system.
  • Urination in the shower must be avoided (common with young boys).
  • Laundry water from clothing badly soiled with excrement, blood, or vomit should be bypassed to the sewer system.
  • Do not spit into hand sinks if plumbed into the gray water system.
  • Avoid water from bathing a dog, flushing an aquarium, or cleaning a pet's cage.
  • The addition of rainwater helps dilute and "sweeten" household gray water.
  • If you think your stored water is getting a little sour: chlorinate it with liquid laundry bleach to 25 ppm (1 gallon of household bleach for 2,000 gallons of water). Let it stand for several days while the chlorine does its job and the bleach odor dissipates.

Project Showcase

Gray Water picture

Blue Beacon Truck Wash (California): Recycling gray water in an underground tank for reuse / 8000 gallons

Steger Residence (Minnesota): Landscape and garden irrigation / 8,000 gal.

Cooper Hospital (New Jersey): Backup nonpotable water / 25,000 gallons

Thomas Bell Center (New Mexico): Combination of gray water and rainwater used for landscape drip irrigation / 12,000 gallons

Choosghai School (New Mexico): Gray water for toilet flushing / 10,000 gallons

NC State-Dole Nutrition Center and UNC Laboratories (North Carolina): Gray water reuse - recycling restroom sink water for toilet flushing / 8,000 gallons


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