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'''Greywater''', sometimes also spelled as '''graywater''', '''grey water''' or '''gray water''', is water that has been polluted with (non-)biodegradle soaps and detergents. It hence comprises the water from all rooms of the household, except that from the [[Bathroom Toilet Unit|toilet]]s.
'''Greywater''', sometimes also spelled as '''graywater''', '''grey water''' or '''gray water''', is water that has been polluted with (non-)biodegradle soaps and detergents. It hence comprises the water from all rooms of the household, except that from the [[Bathroom Toilet Unit|toilet]]s.
It is important to treat blackwater from greywater seperatly, as the latter is less polluted and so requires less treatment steps. By having less quantity of water going trough less treatment steps the treatment procudure becomes more efficient and less costly.


The water leaving our homes carries [[nutrients]]. The water itself is also of value, an increasingly limited resource especially in dry climates. It may also contain [[pathogens]], and/or harsh chemicals and care should be taken with it; although it is not as great a health risk as [[blackwater]] ([[sewage]]), it should be handled with great care and human exposure to greywater should be avoided.  
The water leaving our homes carries [[nutrients]]. The water itself is also of value, an increasingly limited resource especially in dry climates. It may also contain [[pathogens]], and/or harsh chemicals and care should be taken with it; although it is not as great a health risk as [[blackwater]] ([[sewage]]), it should be handled with great care and human exposure to greywater should be avoided.  

Revision as of 09:48, 2 October 2012

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Greywater, sometimes also spelled as graywater, grey water or gray water, is water that has been polluted with (non-)biodegradle soaps and detergents. It hence comprises the water from all rooms of the household, except that from the toilets.

It is important to treat blackwater from greywater seperatly, as the latter is less polluted and so requires less treatment steps. By having less quantity of water going trough less treatment steps the treatment procudure becomes more efficient and less costly.

The water leaving our homes carries nutrients. The water itself is also of value, an increasingly limited resource especially in dry climates. It may also contain pathogens, and/or harsh chemicals and care should be taken with it; although it is not as great a health risk as blackwater (sewage), it should be handled with great care and human exposure to greywater should be avoided.

Redirecting the water we use for tasks such as showering allows us to reclaim some of that value to grow plants and recharge the water table. It may be necessary to choose our soaps and detergents more carefully, if we use the greywater for watering and fertilizing plants.

Recycling

Systems

At present, several water recycling systems exist which can be used to:

  • recycle the water without purifying it
  • recycle the water while purifying or decontaminating it

Water recycling systems without purification

Water recycling without purification is used in certain agricultural companies (e.g., tree nurseries) and dwellings for applications where potable water is not required (e.g., garden and land irrigation, toilet flushing). It may also be used in dwellings when the greywater (e.g., from rainwater) is already fairly clean to begin with and/or has not been polluted with non-degradable chemicals such as non-natural soaps (thus using natural cleaning products instead). This water system also needs a supply of water to recycle and reuses water as well. It is also not recommended to use water that has been in the greywater filtration system for more than 24 hours or bacteria builds up affecting the water that is being reused. Water purification/decontamination systems then again are used for applications where potable water is required (e.g., to allow drinking, and/or for other domestic tasks as washing, showering).

Water recycling with purification

For filtering the water to become potable (or near-potable), there are numerous systems based on soft processes. These include natural biological principles such as

Finally, "hard", direct processes, such as distillation (evaporation) or mechanical processes such as membrane filtration, (typically ultrafiltration and reverse osmosis, which are capable of treating high volumes of grey water) can create potable, or near-potable water. There seem to be no commercially available "hard" greywater recovery devices suitable for on-site use in the individual household, even though a number of such technologies exist.

In order to purify the potable water adequately, several of these systems are usually combined to work as a whole. Combination of the systems is done in two to three stages, using a primary and a secondary purification. Sometimes a tertiary purification is also added.

Some municipal sewage systems recycle a certain amount of grey and blackwater using a high standard of treatment, providing reclaimed water for irrigation and other uses.

Minimizing health risks from greywater

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  • Wash yourself after contacting greywater.
  • Install signage around greywater irrigation systems or areas.
  • Do not drink or play with greywater.
  • Do not allow anything that may be eaten to come into contact with greywater.
  • Do not allow greywater to pond or run off the property.
  • Do not wash domestic pets in greywater or allow pets to drink greywater.
  • Do not use greywater in public places such as children's play areas or playgrounds, BBQ areas or recreation facilities.

Suggested projects

  • What is the effect of various detergents and soaps in a greywater system? Consider the receiving soil and plant types - the answer may vary.[expansion needed]

Organizations

Projects

External links

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