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Using Grey Water in the Home

Using grey water around your home is a great way to reduce your reliance on the city water supply and save water at the same time.  However, it is important to get it right in order to keep your family and pets safe and prevent damage occurring to your soil or plants.  We’ve put together everything you need to know.

Types of Grey Water

Grey water can come from the bathroom, kitchen or laundry.  Bathroom grey water consists of the water that comes from the bath, shower or hand basin, and is the least contaminated form of grey water.  However, it is still contaminated with soaps, shampoos, hair dyes, toothpastes, cleaning products etc.

Laundry grey water improves in quality as the washing machine moves through the cycle, making the rinse water the cleanest.  If you plan to use the water from the wash cycle, be cautious as the chemicals, suspended solids, lint and turbidity can pose problems. 

Kitchen grey water is the most contaminated form and should always be treated before being used.  This is because it contains food particles, oils, fats, chemical pollutants and other waste. 

Using Grey Water

When you are using your grey water, it is important that it is not stored for more than 24 hours if you don’t have a treatment system.  Divert the water directly to the garden using an irrigation system such as an underground one.  You should not hose with grey water as this spreads chemicals and bacteria, and untreated grey water can only be applied underneath the soil.  Never water your vegetables or other edible plants with grey water as it may be a health hazard.

If you have a native garden, take care to use laundry detergents that are low in phosphorus.  Native plants can be very sensitive to high levels of this chemical.  All laundry detergents should be low in salts.

It is important that the grey water does not run off onto the street or onto the neighbours’ property.  They are allowed to lodge a complaint with the council if this happens.

Grey Water Devices

The two main type of grey water devices are gravity diversion and pump diversion.  In gravity diversion devices, the grey water is diverted from a plumbing fixture straight on to the garden.  This flow is commonly activated by a tap or switch and it must be piped to the garden through sub-soil irrigation.  In wet weather, the water is diverted to the sewage system.

Pump diversion devices work similarly to grey water devices but they also have a surge tank to control the flow of water to the garden in the case of sudden surges.  Do not divert your kitchen water through a surge tank as fats, oils and food particles can clog the system, potentially creating odours and causing the sub-soil irrigation system to malfunction.  Surge systems also should not be used as a storage tank.

If you are using a grey water diversion device, the grey water must be used immediately and not stored.  You will also need to meet the minimum maintenance requirements that have been set by your local council and ensure that it meets health and plumbing requirements.

Grey Water Treatment Systems

Domestic grey water treatment systems are designed to collect, store and treat domestic grey water.  Such systems may include wetlands, intermittent sand filters, soil filters, grey water septic tanks, and aerated waste water treatment systems.

The treatment process will differ according to the way that the grey water will be used.  Processes may include settling of solids, flotation of lighter materials, anaerobic digestion by bacteria in a septic tank, aeration, clarification, and disinfection.  Primary treatment only reduces the amount of solid material in the water so secondary treatment is required in order to remove the pollutants from the remaining liquid.

The disinfection of the water is the final stage of the treatment process and is used to eliminate bacteria that may be dangerous (called pathogenic bacteria).  It is important to use the disinfection process if people, animals or insects will come into contact with the water.  If you choose not to disinfect the water, the water will need to be at least 100mm below the soil level.

Safety Issues with Grey Water

There are a few steps that you will have to take to ensure that your grey water system is safe.  To ensure that your drinking water remains clean, be sure that there is no cross connection between your grey water system and the water supply.  This is possible if you use grey water to flush the toilet but installing a backflow prevention device will reduce this risk.

Always maintain a connection to the sewer to stop grey water from spreading during wet weather.  Contact your local council to find out their requirements before installing a treatment system or distributing grey water throughout the garden.  Finally, if you are making any changes to your home’s plumbing system, it is vital that this work is carried out by a licensed plumber.

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