Grey water is water that is collected after use in household washing machines, hand basins, showers and baths. Grey water does not include water from toilets, which is referred to as ‘black water’.
Grey water is a valuable resource that can be used to irrigate your lawn and garden, particularly in times of drought and when water restrictions are in place.
Below is some general information on using grey water on your lawn and around your garden, however before use, please check with your local council or water authority for their latest guidelines. In some areas, untreated grey water can only be used in sub-surface irrigation systems.
Where to use grey water
Grey water can be used to irrigate your lawn, as well as ornamental (non-edible) plants. Avoid using grey water around Australian native plants, which can be sensitive to the phosphorus in some detergents. Potted plants shouldn’t be watered with grey water regularly either, due to the potential build-up of salts.
How to use grey water
Grey water can be collected in buckets or tubs (kept away from babies and children) or diverted straight from the washing machine using a grey water hose. Significant amounts of water can be re-used if directed out onto your lawn and garden. According to Sydney Water, water use in showers and baths totals 32%, and 12% in washing machines, in an average home (http://www.sydneywater.com.au/SW/your-home/saving-water-at-home/garden-and-pool/index.htm).
Allow your grey water to cool down before use, and ensure you change the spot where you use it, so that the same section of lawn is not overloaded. A handy way to remember is to move grey water hoses from one spot to another on the same day each week – we do it on Sundays!
Which detergents are suitable for grey water
It’s important to choose laundry detergents that are low in salt, phosphorus and are pH neutral, so that your lawn and plants aren’t harmed and the pH of your soil isn’t altered. Alkaline soil can lead to nutrients becoming unavailable, particularly iron. High concentrations of salts can also damage your lawn and plants, and lead to burnt growth and poor health. If your lawn or plants that have been irrigated with grey water start to develop any discolouration, discontinue use in that area.
Check detergent labels for information about whether it’s suitable for grey water usage. Some laundry detergent manufacturers recommend only using washing machine rinse water to irrigate the garden and not the wash cycle water, so this needs to be taken in account when using grey water.
Don’t store grey water for more than 24 hours, as it can become a source of infection and can start to smell.
Additional information on grey water
- There are specially designed treatment tanks that households can install to process grey and black water. These are basically small domestic sewage systems that aerate waste water and bacteria breaks down the solid waste, before the water is then pumped out onto the lawn/garden. There are multiple companies that sell and install these aerated wastewater treatment systems.
- Do not use grey water when family members are ill with a gastrointestinal infection, or from the washing machine when washing dirty nappies.
- It’s best not to allow people or pets to walk or play in areas that are being irrigated with grey water. Leave the area to dry for a few days before allowing people and pets back onto the area. This helps reduce any contact with potential sources of bacteria and infection that may be in the grey water.
- Using untreated grey water from the kitchen is not recommended, as it can contain a high level of oils. Oils can adversely affect soil structure and contribute to soil becoming water repellent. However, you can rinse your fruit and vegetables over a bucket in the sink and use that water on your lawn.
- You can also place a bucket under the shower and collect the cold water before it runs hot. This valuable water would normally be lost down the drain and can be used to water pot plants (as it does not contain any detergents or soaps) and garden beds.