Definition of Grey Water

What Is Grey Water?


Grey water (spelled alternately as greywater or gray water) is the recycling of ‘waste’ water that is generated in homes and commercial buildings through the use of water for laundry, dishes, or for bathing. Grey water differs from black water which is wastewater used in toilets and designated for sewage systems. Grey water can be used for a variety of purposes such as irrigation or toilet flushing and is collected from:

  • Sinks
  • Showers
  • Bathtubs
  • Washing machines
  • Dishwashers

Grey water collection and distribution systems can be simple or complex. The basic components of a grey water system include:

  • Diverters: Connected to water pipes to direct waste water from indoor systems into the grey water system
  • Overflow: Prevents grey water from overloading the system by directing excess into the sewer system
  • Filter: Can be added to remove soap, food particles, dirt and sand, debris, and other larger contaminants from the grey water
  • Distribution: Used to direct grey water into toilets or an irrigation system. Can include drip irrigation or subsurface irrigation trenches for landscaping, and so on
  • Surge tank: A temporary holding vessel for containing water until it is needed
  • Pump: For pushing grey water through the distribution network, though some rely solely on gravity
  • Treatment: A filtration system to further purify grey water by removing any remaining contaminants to make grey water suitable for irrigation

Some concerns have been raised with the use of grey water for irrigation and so on. For instance:

  • Water from kitchens can contain levels of fat, food residue, and other contaminants
  • Bathroom grey water can be contaminated with non-biodegradable soaps and other personal care products
  • Laundry detergents and dishwasher detergents that are high in phosphates and other chemicals can have a negative impact on the environment when used as grey water
  • Water used for washing dirty diapers and other sanitary products can contain human waste which poses health problems for the use of this grey water

However, many grey water systems can be designed to overcome these concerns and make use of the valuable resource that is grey water. There are many benefits to installing a grey water system in your home or building:

  • Provides locally-generated water
  • Lowers requirements for extracting water from local water systems
  • Reduces impact on sewage and septic systems
  • Is a means for recharging groundwater systems
  • Reduces the energy needed to convey water through conventional systems
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