Using greywater

Greywater is the waste water from showers, baths, spas, handbasins, laundry tubs, washing machines, dishwashers and kitchen sinks. It doesn't include water from toilets — that's called black water. With water restrictions in many areas, using greywater on your garden could help save hundreds of litres of water a day.

Washing machines account for almost a quarter of household wastewater or, depending on your machine, about 60 to 180 litres per wash. So washing six times a week could send more than 1000 litres down the drain in one week alone. Add to that your dishwashing, shower and bath water, and you're soon up to 4000 litres a week for the average family of four.

Using greywater:

• Greywater can be stored and used on the garden (or even in toilets or washing machines), or else it can be diverted to the garden with a plumbed-in diverter (with a switch so that if it's raining, it goes into the sewer instead). Conditions may apply in the area where you live: contact your local council for advice on options available.
• Don't store untreated greywater for more than 24 hours: if you can't use it (for example, because it's raining) don't keep it.
• If it's untreated, limit usage to water from the shower, bath and washing machine (preferably rinse water). Kitchen water contains fats and solids that might damage soil and plants.
• DIY options include attaching an extra-long flexible hose from the washing machine to the garden or using a bucket. Don't leave buckets lying around if you have small children because they're a drowning hazard.
• If someone in your family is sick with gastro or flu or another contagious disease, stop using the greywater.
• Don't water herbs or vegetables, or pot plants.
• Keep the greywater underground, or under mulch — this helps prevent evaporation, as well as keeping it away from kids and pets.

• CHOICE has completed a test report for recommendations on laundry detergents to use. Read details of the CHOICE report.
• The components most likely to cause problems are phosphorus, salinity, sodium and pH.
• All laundry detergents contain salts and are highly saline. Frequent long-term use would likely harm your garden, unless it was spread over a large area. Sodium in the salts is particularly detrimental not only to plants, but soils. It affects the soil's permeability and causes a loss of structural stability.
• Laundry detergents are highly alkaline (that is, have a high pH): a pH higher than 10 helps dissolve organic dirt, such as grease, oils and food scraps. Most biological systems prefer a pH between 6 and 9, and greywater with a high pH is likely to harm many plants and soil organisms.
• The larger the irrigation area (minimum recommended area is 150 to 200 square metres), the more you'll spread the chemical load.
• Potential impacts are very much dose-dependent — try reducing the amount of detergent you use, providing it still gets your clothes acceptably clean.
• Some laundry detergent products whose names imply they're environmentally friendly could in fact cause problems if used on your garden. See the CHOICE report for more.

• Consult your sewage removal authority if you intend to redirect all or a major part of your used water.
• Consult a licensed plumber for advice on the best system for your needs.
• Inform your water supply authority of any changes to your plumbing.

For lots more water tips and help choosing water-efficient products see the CHOICE water conservation guide.