How much greywater?

The average person uses between 20 and 45 gallons per day for simple tasks such as bathing or showering, and using the washing machine.

This doesn’t sound like much, but over one month this amounts to over 1,350 gallons per person.
In a new house, with new appliances and plumbing fixtures, this figure may drop to about 25 gallons per day, or 750 gallons per month.

How much graywater do you produce?
This varies from house to house. For most cases, about 60% of water used inside the home would be considered graywater. However, this is largely dependent on personal hygiene practices.

As an example, the national average shower usage per person per day is 11 gallons. Yet the average shower using hi flow shower heads (5gpm) is 35 gallons, and low flow is 20 gallons.

Combining the two statistics above would mean the average American showers every 2-3 days!

Practical Graywater Re-use
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 (basin) 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 not irrigated in the garden. In addition to containing high bacteria levels, the significant quantity of fats can create an impervious barrier within the top soil.
  • The dishwasher does not empty into the kitchen sink waste, because the detergent is too caustic.