If you want to re-use your greywater, you need to be careful of the washing agents used.


Salts (sodium sulphate) are a by-product of the manufacture of washing agents. They are included in powders as filler. There are generally less salts in concentrated powders, and even less in liquids. There is information available online that can be used as a guide to the sodium content of washing agents at www.lanfaxlabs.com.au. Excess sodium in a clay soil can be amended with the addition of gypsum and compost.


Too much phosphorus in greywater can be toxic to native plants, proteas and cause pollution of our waterways. It can also cause iron deficiencies in plants. Choose a washing agent that has low phosphorus. The Lanfax Labs website may be used as a guide to phosphorus levels in washing agents.


Greywater can raise the pH, in other words, make the soil more basic (the opposite of acidic). This will tend to cause iron deficiency in plants, seen as yellow new leaves, sometimes with green veins. If you notice these symptoms, you should have the soil around the affected plant(s) tested. If the pH is high, sulphate of iron treatments will gradually reduce the pH.


Bleaches (such as hair dyes and nappy wash) and disinfectants (including eucalyptus and tea tree oil) can detrimentally affect the health of soils by killing soil organisms.


If you are using shower or bathwater on the garden, fats from soaps can make the soil water-repellant. The soil will benefit from an application of a soil rewetting agent every 6 months.

For information on the sodium and phosphorus content of common laundry powders and detergents, see Patterson, R.A. (1999) Laundry products research, Lanfax Laboratories, Armidale, NSW. www.lanfaxlabs.com.au