Grey water can be a valuable source of water to use in the garden, particularly during dry conditions. Learn how and where to use grey water at your place.

 

Grey water is water that comes from household washing machines, hand basins, showers and baths.  Grey water does not include water from toilets, which is referred to as ‘black water’. 

When used correctly, grey water has the potential to irrigate lawns and gardens. This helps make the most of precious water resources, particularly during times of drought and water restrictions. Consult your local council or water authority for the latest regulations regarding grey water usage in your area. In some areas, untreated grey water can only be used in sub-surface irrigation systems.

However, here is some general information on using grey water in your garden.

 

Where to use grey water

Grey water can be used to irrigate the lawn and ornamental (non-edible) garden beds. Grey water should not be used to irrigate herbs and vegetables or any food that will be consumed raw. Avoid using grey water around Australian native plants, which can be sensitive to the phosphorus in many detergents.

Potted plants should also not be watered with grey water, 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 an appropriate grey water pipe or hose. According to the SmartApprovedWaterMark, 15-20% of water used in homes is in the laundry  (https://www.smartwatermark.org/smartwateradvice/saving-water-home/laundry/) . Large top loading washing machines can use up to 170 litres of water per cycle, which is a significant amount of water that can be directed out into the garden.   

It’s best to regularly move grey water hoses around the garden and lawn so the same plants / areas are not being constantly watered with grey water. A handy way to remember is to move grey water hoses from one spot to another every weekend.

Which detergents are suitable for grey water

It’s important to choose laundry detergents that are suitable for using in grey water. Detergents contain phosphorus and salts that can harm some plants and affect the quality of the soil or increase the soil’s pH (make the soil more alkaline). Soil with an alkaline pH (pH greater than 7) can lead to nutrients becoming unavailable to plants, particularly iron. You may start to see plant leaves becoming pale with dark green veins, which indicates an iron deficiency. High concentrations of salts can also damage plants and lead to burnt leaves and poor plant health. If plants irrigated with grey water start to develop pale or discoloured leaves, discontinue using grey water in that area.

Look on detergent labels for information about whether it’s suitable for grey water usage. Product labels may say ‘Grey water safe’ or ‘Grey water friendly’. 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 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 higher levels of oils . Oils can adversely affect soil structure and contribute to soil becoming water repellent. However it’s a great idea to rinse fruit and vegetables over a bucket in the sink and collect that water to use in the garden.
  • 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.

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Saving Water in your Garden

With the dry conditions in Australia it is important that we know how to care for our gardens and especially when there is limited water supply. It’s a precious resource that we all need to protect.


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