Safe uses for greywater
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Kevin and Jo Lester, via email
We love our garden and we’d like to use our greywater to help get some of our plants through the dry times. What do we need to know about using it?
Phil Dudman says
Handled correctly, much of your household greywater can be put to good use in the garden, potentially saving thousands of litres of town or tank water. However, greywater may contain harmful pathogens and salts, so misusing it can pose a serious health risk to humans, soil and plants. Here’s what you need to know, but before using greywater in the garden, check if your local council has any other guidelines or restrictions.
• Use only the best quality greywater from the bath, shower, hand basin and final rinse of the washing machine. • Don’t store untreated greywater. Use it as soon as possible to avoid offensive odours and dangerous build-up of harmful bacteria, and if you can’t, divert it to the sewer. • Always apply greywater directly to mulched garden beds. Don’t spray it in the air as you don’t want anyone having contact with it.
• Use untreated greywater on trees, shrubs or ornamental perennials. • Don’t use greywater on any of your vegetables, ground-dwelling edible herbs or potted plants. • Untreated greywater is safe to use on fruit trees, but not on trees where fruit that falls may be eaten. • Don’t use greywater in areas where children and pets play.
• Don’t allow greywater to run off into stormwater drains or neighbouring properties. • Avoid irrigating with greywater within 1m of any boundary lines, buildings, in-ground pools and in-ground potable water tanks. • Don’t allow greywater to pollute drinking water or groundwater, or to enter a watercourse.
• Don’t use greywater during rain or when the soil is saturated. Only use it when the garden needs it. • Don’t allow greywater to pool on the surface of the ground. • Don’t use greywater from the washing of nappies or soiled clothing, or when someone in the house is sick or has diarrhoea. • Wash your hands thoroughly after contact with greywater. If you’re serious about the ongoing use of greywater, look into some of the diversion systems that help to automate the process and reduce contact, as well as systems that treat the water and improve the quality, further reducing risk. Keep in mind that many soaps, shampoos, washing powders and detergents contain high levels of nutrients and salts that will harm soil, plants, groundwater and waterways. Look for the washing and personal hygiene products that are low in nitrogen, phosphorous and salts, sometimes labelled ‘greywater safe’ or ‘garden safe’. If you’re unsure of the safety of a product you’re using, don’t use that batch of greywater.