How to safely reuse laundry water to water your garden - Run Greener (2024)

Reusing greywater is a great money saving alternative to provide a water source for pot plants, lawns and gardens. Before you jump straight into it, keep reading to find out the safe and most efficient way to make the most of reusing greywater.

Escherichia coli (E. coli) is a type of bacteria that is commonly used as an indicator of microbiological quality. E. coli is naturally found in the gut lining of humans and other animals. It is present in faeces and therefore be used to indicate contamination of harmful microorganisms that can cause illness or infection when a high level of E. coli is detected in greywater. Generally, greywater from bathrooms and laundries usually have low counts of E. coli however are usually higher when greywater is contaminated from washing nappies or clothes soiled with faeces or vomit.

Conventional household cleaning and beauty products like detergents, laundry powder, shampoos and soaps contain chemical compounds such as nutrients and salts that can be harmful to the environment in high concentrations. Greywater reuse systems disperse untreated greywater via subsurface (below ground level) irrigation at a constant rate. By doing this, it reduces the risk of contact with untreated greywater that may contain microorganisms potentially capable of transmitting disease and prevent overloading of salts or nutrients in one specific area.

Hand watering large volumes of greywater from a bucket can cause excessive nutrient loading in a single area causing damage to soil, plants and groundwater (in high water table areas). Greywater watering on topsoil can also cause runoff to off-site waterways like stormwater drains leading to rainwater catchment areas and natural rivers and lakes. Excessive nutrient loading from fertiliser runoff is a huge problem in both man-made and natural waterways.

An accumulation of salt concentration can affect soil structure including the ability to absorb water and causing problems with plant growth and degradation to vegetation. Using eco-friendly laundry and bathroom products or even DIY recipes can reduce the amount of salt that leaches into the soil from using a greywater reuse system. Other ways to help with soil sodicity is to incorporate organic matter into the soil through mulching or adding lime.

Untreated greywater can be used safely to water your garden through a greywater reuse system (greywater diversion device) however should not be used by capturing waste water in buckets and manually watering plants. There is a risk of disease being transmitted when pathogenic microorganisms in untreated greywater is transferred through direct contact methods such as contaminated hands, inhalation of greywater spray and contact with broken skin. Indirect contact methods with greywater can also occur including coming in contact with contaminated items (e.g. toys, gardening equipment) and areas (e.g. grass or soil) and through contact with pests (e.g. mice, rats, flies, co*ckroaches) or pets.

Subsurface irrigation reduces the exposure of untreated greywater to pets, pests or any other animals that would otherwise come in contact with the untreated greywater on the soil surface. Regulations are set in place for irrigation of untreated greywater to ensure minimal risk to public health including:

• Greywater diversion device is located away from buildings, boundaries, water sources (e.g. bores), water bodies (e.g. swimming pools, ponds);
• greywater is not to be reused for edible ground vegetable or plants; and
• ensuring the irrigation field is only located within the property boundary.

There are greywater resuse systems that are designed to provide surface (above ground level) and subsurface irrigation that treats greywater to a higher quality called a Greywater Treatment System (GTS). Greywater from these systems is disinfected and also acceptable for use in areas around the home including toilet flushing, providing cold water supply in washing machines and water storage available in a holding tank.

First things first, you should learn about how to reuse greywater and what is in greywater that may have an effect on your garden. Just like the fertiliser that we apply to our lawns, the pH of greywater tends to be slightly alkaline due to the phosphate content in washing detergents and soaps. The pH of greywater can range between 6.5 and 10.5 which means that the area in and around an irrigation field from a GDD can cause the surrounding soil to be more alkaline. So how can high alkalinity in soil affect the plants in your garden? Different plants like soil that is slightly acidic or slightly alkaline however plants typically grow best in neutral or slightly acidic soil and most won’t thrive in soil that is highly acidic or highly alkaline. Some shade loving and acid loving plants like azaleas, camellias, gardenias, begonias, blueberries and ferns will not grow well in high alkalinity soil from greywater.

Fillers in washing powders that contain sodium salts can increase the salt content in greywater and high levels can result in poor soil structure and can damage plants by reducing the drainage capability of plants. Liquid detergents that contain potassium salts or eco-friendly detergents can be used as substitutes to improve the quality of greywater by reducing the salinity.

Use eco-friendly cleaning alternativesand avoid the use of harsh chemicals including bleach, borax, sodium perborate, sodium tripolyphosphates (STPP), phosphorus (phosphates, polyphosphates, phosphate builders etc), acids and drain cleaners.

The take home message: you can and should reuse greywater but do it right! To start small, here are a few Do’s and Don’ts for bucketing greywater:

• Karen G
• 17 May, 2020