Grey Water Use

By   August 2, 2011

Grey water should be used with care, but can be useful in times of water shortages.

Plants can be watered with shower, bath, kitchen and washing machine water (from rinse cycles), collectively referred to as ‘grey’ water. It varies in quality and may contain contaminants such as soap and detergent. Fortunately, soil and potting composts are effective at filtering them out, and the residues can sometimes act as a mild fertiliser.

To minimise bacterial growth, grey water should only be saved for 24 hours, unless filtered through a reedbed or professionally-designed system. It is best applied by watering can; grease and fibres can clog irrigation systems.

There should be no problem with small-scale, short-term use of grey water to tide plants over in summer drought. An exception is on edible crops, due to the risk of contamination from pathogens in the water.

Long-term, extensive use, or permanent altering of indoor plumbing should not be attempted without expert advice.

Softened tapwater and dishwasher water are less useful. Salts used in them can damage soil structure, particularly if rich in clay. This said, short-term use of softened water should not cause serious damage and may be worth considering in an emergency.