Islands For Sale Islands For Rent Blog Magazine PII



Grey Water Treatment

Wednesday, December 7th, 2011

Reed Bed

What is Grey Water?

On islands the waste that is produced from washing machines, sinks, dishwashers and other appliances is known as grey water or sullage. Grey water comprises about 50-80% of water used in the home and it differs from black water which is primarily composed of chemicals and biological contaminates such as feces. Many island owners use a septic system that collects and treats both black and grey water. Other island owners choose to keep there black and grey water separate, instead opting to treat their grey water and return it back to the natural environment.

How is Grey Water Recycled?

Since grey water is less contaminated than black water it is much easier to treat and recycle. Nonetheless, grey water is still a pollution and health hazard and should always be treated before domestic use.

There are a number of ways that grey water can be treated on islands using natural biological principals. These natural or “soft” island grey water filtration systems include reed beds and living walls.

A reed bed is an artificial wetland constructed to provide small scale sewage treatment. The grey water trickles through the reed bed and is rapidly cleaned by the extensive root systems and its associated microorganisms who use the sewage for growing. The result is an extremely clean effluent.

Living WallA living wall is a vertical garden where plants are rooted in a fibrous material which is anchored to the wall. Grey water trickles down between the sheets and feeds the moss, vines and other plants. Bacteria which grow on the roots metabolize impurities. More advanced living walls may also use insects, fish and salamanders for water treatment. Living walls are ideal for smaller islands where space is a concern and on arid islands since the circulating water on a vertical wall is less likely to evaporate.

There are also ways that grey water can be treated using “hard” or direct process. These technologies usually rely on processes such as distillation. Despite these technologies being available they are not viable for small scale residential use and therefore are impractical for islands.

It is important to remember that the grey water is treated before storing it for purposes such as irrigation. Letting the grey water stand will increase the number of pathogens and bacterium in the water.


There are numerous environmental and practical benefits to using grey water on islands. Using grey water treatment reduces the amount of freshwater removed from rivers and aquifers, reduces dependency on septic tanks, recharges groundwater and aids in plant growth. In addition, if you need to ship water to your island it helps you conserve and reuse your water therefore saving you money.

Government Regulations:

Government regulations regarding grey water treatment and usage are still being developed in most areas. Since it is a relatively new technology there is some uncertainty about the long term benefits and risks of grey water.

Grey water is considered in most areas to be sewage. Therefore there are regulatory procedures enacted to ensure this water is properly disposed of to prevent the spreading of diseases and pollution. Thus in these regions this means that grey water diversion has simply be not permitted or has been discouraged.

Therefore before installing a treatment system check to ensure there are no laws preventing the building of grey water treatment system.


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