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White, Grey and Black Water
Water used in the home and in commercial premises
is now classified as “white”, “grey” or “black”.
One purpose of this classification is to indicate whether water can
be safely reused or recycled within the building.
White water is drinkable water, generally purified and
supplied through a mains supply.
Grey water may be rainwater that has fallen from the sky and been collected.
Although it may be low in contaminants, it is not safe to drink.
Grey water may also be white water that has been used in a washing machine or bath.
Both types of grey water can safely be used for non-drinking purposes,
such as flushing a toilet or watering a garden.
Grey water will need to filtered and purified if it is stored for more
than 24 hours, and will need its own, separate pipe network,
so there is no risk of contaminating the white water supply
or of promoting bacterial growth, particularly legionella,
which can cause the potentially fatal Legionnaire’s Disease.
Black water is water that contains biological matter,
particularly from flushing toilets. This is always disposed of,
usually to a main sewage treatment works, where it can be purified, although
alternative technologies such as bio reactors and reed beds are sometimes used.
Grey water which is not recovered is also piped away to a sewage treatment works.