Grey Water Overview

Grey water is wastewater generated from baths, showers, washbasins, and laundries. This water can be diverted for use on lawns and gardens, making it a sustainable choice for tiny house living in Australia.

Using Grey Water in Tiny Houses

To divert grey water from laundries and bathrooms, you can:

• Use a bucket to manually remove untreated grey water (excluding kitchen grey water).
• Connect a flexible hose to a washing machine outlet.
• Have a licensed plumber install a grey water diversion device or grey water treatment plant (with local government approval).

Kitchen Grey Water Considerations

Kitchen grey water is not suitable for use in sewered areas due to grease and oil from the sink, which can clog plumbing. In unsewered areas, ensure kitchen water passes through a grease trap first.

Storing Untreated Grey Water

Do not store untreated grey water. After 24 hours, stored untreated grey water may:

• Turn septic
• Emit offensive odours
• Promote the growth of microorganisms
• Breed mosquitoes

Ensure there’s an option to divert grey water to the sewerage system if it’s not practical to use it immediately (e.g., during wet weather).

Safe Use of Untreated Grey Water

Use grey water with care to avoid health hazards or nuisances such as ponding or run-off onto neighbouring properties. To prevent issues, opt for ‘below ground’ irrigation systems, which can be designed to suit soil and garden conditions.

When establishing a grey water system:

• Prevent grey water from entering swimming pools or flowing into neighbouring properties.
• Avoid ponding, unpleasant odours, or plant damage by managing the outlet’s location and usage.
• Keep grey water away from children’s play areas.

Grey Water Diversion Devices

A grey water diversion device can redirect grey water to an irrigation system. These devices often include a filter to screen out hair, lint, and other solids. The device must:

• Be fitted with a switch to divert grey water to a subsurface or surface irrigation system.
• Automatically divert grey water to the sewer in case of a blockage.
• Have WaterMark approval and comply with plumbing laws.
• Be installed by a licensed plumber.

Control irrigation based on the volume and type of grey water diverted. Check local council approval requirements before installing a grey water diversion device.

Grey Water Treatment Plants

A grey water treatment plant collects, stores, treats, and disinfects grey water to specific standards, suitable for both sewered and unsewered areas. Refer to the Queensland plumbing and wastewater code to see the treatment levels required for specific end uses. Potential end uses include:

• Flushing toilets
• Providing water to the laundry (e.g., cold water source for washing machines)
• Washing vehicles
• Cleaning paths and walls
• Irrigating lawns and gardens

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Why Install a Grey Water System?

If you’ve been thinking about how to make your home more eco-friendly and save water, a grey water system is an excellent way to reuse and save thousands of litres of water annually.

Think about how often you turn on the taps in your home—every time you wash your hands, start the shower and wait for it to get warm, rinse a dish, or run the washing machine. Hundreds of litres of perfectly usable water are washed away from your home, into storm drains, and then onto treatment plants, where it’s often diverted back into the ocean, river systems, or creeks around your city or town.

If you’ve ever experienced water restrictions implemented by your local council, you know how precious water is. Grey water systems enable you to take control of the water you might otherwise waste and use it around your home instead of letting it flow away.

Understanding Grey Water

Grey water is any untreated water that hasn’t come into contact with a sewer system, which includes water from your shower, laundry, kitchen, and bathrooms (excluding the toilet). This water is classified as grey water.

Kitchen Grey Water Note

Depending on your grey water system, it’s usually advisable to have a grease trap if you’re including kitchen grey water. Kitchen water contains fats and oils from cooking that can harm the soil and plants and clog leach lines and connections. The grease trap helps reduce these issues.

Ultimately, the type of grey water you use in your backyard will be determined by what you put into your water and how you filter it. Using harsh chemicals and soaps in your washing (like bleach, bath salts, chlorine, acids, and anything containing boron) can impact your grey water’s usefulness without proper filtering. The two major factors affecting the health of your soil are salt and pH levels.

Salt

Salt build-up in your soil can be particularly harmful. Many powdered detergents and fabric softeners use sodium salts as a bulking agent, so it’s worth checking the ingredients before buying. Look for low-sodium washing powders, concentrated powders, and liquid detergents, as these tend to have less sodium.

pH Levels

The types of plants in your garden will determine if you need more acidic or alkaline soil. Monitor the pH levels of your garden, especially if you’re using grey water on fruits, vegetables, and herbs. Shower water tends to be neutral, while washing machine water is often more alkaline.

Other Considerations

Besides salt levels and pH structure, some oils and fats can negatively impact your soil, particularly those from shampoos using eucalyptus or tea tree oil and some toothpaste.