101: About Graywater

The average person produces between 25 and 40 gallons of graywater per day.
For New Home Construction, the best sources of graywater are showers, laundry and tubs.
A 20,000 gallon rainwater tank would be required (at a much higher cost) if rainwater harvesting was used instead of an IrriGRAY graywater system with 3 residents.

Graywater (also spelled Greywater) is a fantastic resource, because we produce it EVERY day.

The average person generates 25 to 40+ gallons graywater per day in summer, often much more in drier, hot climates like California, Arizona and Texas.

Now 40 gallons doesn't sound like much, but with 3 people in a house, that adds up to 3,600 gallons per month.

AND when using sub surface dripperlines, together with the sophisticated  control system included with IrriGRAY, 95% of this water is used effectively, compared to less than 50% efficiency with clean water spray irrigation.

In fact, with 3 residents in a hot climate,  the IrriGRAY system provides as much irrigation water as a 20,000 gallon rainwater tank, at a fraction of the cost.

So, even if you are in a very dry, hot and dusty location, you can have the landscape you want, while saving water and money every year.

The supporting math for rainwater vs graywater comparison is: 

  • 3 people x 40 gallons per day x 30 days = 3,600 gallons, with 98% irrigation efficiency.
  • Rain is sporadic over summer, so at least 3 months storage is required (usually more). Therefore multiply graywater 3,600 x 3 months = 10,800 gallons.
  • Most rainwater harvesting systems use sprinklers or hose irrigation, and are typically 50% efficient, so multiply the graywater amount 10,800 x 2 = 21,600 gallons.

Types of Graywater

Graywater is household waste water that includes the following:

  • Shower Water
  • Bath Water
  • Lavatory (basin) Water
  • Laundry Water
  • Untreated Spa Water
  • Air conditioning Condensate Water

Blackwater is household waste water that includes:

  • Toilet Water
  • Kitchen Water (including the dishwasher)
  • Laundry Water, if the waste water is from washing diapers, or other materials containing feces

The above definitions can be applied generally throughout the world, although exact definitions vary from country to country, and in the US from state to state.

With New Home construction, with new low flush toilets, we recommend lavatory / hand basin waste water still be connected to the black water waste line. This is ensure sufficient water is available to properly flush kitchen and commode(!) solids down the line.