Grey Water

Grey Water System

Grey water is slightly soiled water that accumulates in every household from the shower, bathtub, sink and washing machine. It accounts for up to 50-60% of the total domestic waste water. Unlike rain water it is always available.

All water from these sources is suitable for treatment in a grey-water recovery system. The resulting service water is hygienically safe and suitable for toilet flushing, laundry, garden irrigation, and can be used for commercial applications.

Configuration of a Grey Water Recovery System

greywater systemTo operate a grey water recovery system the grey water must first be collected and fed into the system through a separate plumbing system. The treatment unit consists of two reservoirs: The grey water storage tank and the service-water storage tank. Before the grey water enters the grey water storage tank it passes through a filter for pre-treatment.



Further purification occurs in two steps:

  • Biological treatment: Microorganisms that establish themselves in the grey water tank break down most of the organic matter. This includes soaps, body care products, oils, dander etc. If the system is not in use for an extended period of time, re-establishment of microorganisms can be accelerated with an appropriate product.
  • Physical treatment: A membrane filter assures that the treated water is hygienic. The pore size of the filter is significantly smaller than bacteria and prevents them from passing into the recovered service water.


Other technical components are a device for replenishment of drinking water, a pump to supply the water at the places of use, and controls.

Grey water systems are available for underground installation, or installation in the basement, or utility room. For underground installation a tank-in-tank system is the preferred choice.

Grey Water Applications

Grey water treatment and usage systems have a variety of applications. Ideally the amount of grey water equals roughly the amount of service water needed. Applications are single and multi family homes, hotels, sports facilities, camp sites, businesses and industries. Since a grey water system requires separate plumbing systems for grey water and service water, installation is of special interest in new developments. Under certain circumstances, a combination with rain water collection is advisable.