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What is Gray Water

Sep 27, 2011

What is Gray Water?

Did you know the average person uses 25 gallons of water a day? I’m not talking about drinking water…I’m talking about something known as gray water.

Gray water is defined as household wastewater that comes from showers, laundry water, bath water, lavatory (basin) water, and untreated spa water.

Did you know that 2/3 of the water used in the home can be classified as gray water?…and that is excluding lawn and garden water.

Remember the 25 gallons per day? In a month that can equal 750 gallons of gray water. That is for every man, woman, and child.

Is gray water dangerous?

Graywater (also known as “greywater”) has the potential to carry bacteria and viruses, making it unsafe to drink. In short, greywater is never potable. However, it can be used for things like flushing toilets and irrigation. Untreated, greywater can be unsafe for irrigation via sprinklers as it may cause bacteria and viruses to become airborne.

Rather than wasting Graywater can we recycle it?

The short answer is yes. One of the most widely used methods of recycling gray water is to capture it and use it on plants and gardens. There are other methods for recycling, but a residential graywater recycling system can cost $10,000 or more.

Gardens do not need clean potable water to flourish. In fact many times they thrive on the nutrients that are found in gray water.

There are a few precautions that you should take:

  • Do not store gray water for more than 24 hours.
  • Laundry detergent high in salts can be toxic to plants
  • If you clean using Boron products, do not use water waste for the garden. It too is toxic to plants.
  • Distribute gray water evenly. If you are using a drain hose…like from a washing machine, if you don’t move the hose from time to time you could over water a portion of your garden and kill the plants

For more information about gray water and using it on plants or in your garden, visit this website:

In an urban situation, with a utility provided sewage system, we recommend only re-using shower, bath, spa bath and laundry water. Kitchen and lavatory water is best left for the blackwater waste pipe network. Lavatory water is in most cases does not provide enough water to justify the connection cost, and in any case, provides additional water flow to help flush the blackwater pipe system.

In a rural situation (i.e. a septic system is used), kitchen water can be used (subject to local regulations), IF the following occurs:

  • A grease trap is installed between the kitchen sink and the graywater system. This ensures food scraps, fats and oils are irrigated in the garden. In addition to containing high bacteria levels, the significant quantity of fats can create an impervious barrier within the topsoil.
  • The dishwasher does not empty into the kitchen sink waste because the detergent is too caustic.
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