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Effects of Greywater on Plants, Soil and the Environment
Greywater reuse for irrigation has the potential to save significant amounts of mains water as well as providing fertilisers for your plants.

However, greywater can contain salts, disease organisms, traces of fats and oils (even human body fats), soaps and detergents (which can make the greywater alkaline), and an array of nutrients, some of which could be harmful.

If you intend to reuse greywater for garden irrigation then you should carefully choose the types of household cleaners, detergents, soaps and other chemical products you use.

Effects on Plants

Too much greywater application continuously to one area may cause waterlogging of roots, inhibiting plant growth and even causing plant death. You may find your plants looking unhealthy, or there is evidence of pests and disease on the plants or even obvious discolorisation of foliage.

Some laundry products contain levels of phosphorus which would be detrimental to some native plants, such as Banksias, Grevilleas and Hakeas of the Family Proteaceae. Not all natives are phosphorus-sensitive, but you should try to minimise the phosphorus content of the detergents you use by choosing those that are low in phosphorus.

Greywater tends to be alkaline, which can alter the pH of the soil over prolonged application. Not only does this affect soil properties but it may inhibit the uptake of some nutrients by plants as well as causing toxicity by other nutrients.

Effects on Soil

If greywater is not filtered in some way to remove suspended solids and organic matter, pore spaces in soils can become blocked.

Some laundry detergents are high in salt (typically as a filler in powders) and these will tend to accumulate in the soil profile and cause soil structure collapse. Liquid detergents tend to have much lower salt content.

Excessive fats and oils in greywater sources can make some soils water-repellent, and water may pool or run-off. Generally, the detergent fraction in greywater helps to reduce the natural water-repellency of some Australian soils.

Bleaches, disinfectants and germicides should be avoided as much as possible as these chemicals will kill soil micro-organisms and seriously affect soil health. Even eucalyptus oil and tea tree oil will have the same effect. If you need to use these substances make sure you divert the water to the sewer or use them in a laundry bucket and pour the solution down the toilet.

Effects on the Environment

Excess nutrients may run-off or leach through the soil to enter waterways and aquifers, resulting in algal blooms or other water quality issues. Some types of detergents and optical brighteners are slow to bio-degrade and may persist in the environment for many months.

Want to Find Out More?

In the first instance, contact the Environmental Health Officer at your local council if you have any questions or concerns about greywater recycling at home.

If you wish to find information about the salt and phosphorus content of the household products you use visit www.lanfaxlabs.com.au. Many nurseries and hardware’s supply pH test kits and it is useful to monitor and test the soil for changes in acidity.
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