Graywater - recycling water at home

Graywater is wastewater from non-toilet plumbing systems such as hand basins, washing machines, showers and baths.

When it is handled properly, graywater can be safely reused in the garden. Never reuse water from toilets, water used to wash nappies, or water from the kitchen.

Do not use graywater on vegetables, fruit, herbs or anything else you plan to eat.

Why recycle water#

A typical household uses a large amount of water every day across the bathroom, laundry, kitchen and garden. Showers and washing machines tend to use the most.

Most homes still use clean drinking water for nearly every household task. Some of this precious resource could be conserved by reusing water, and there is growing interest in using graywater for the garden, especially during dry periods and water shortages.

However, there are health and environmental risks if graywater is not used safely. Rules about graywater use vary from place to place, and in some areas approval or a permit may be required. Graywater can be used either treated or untreated, though different conditions apply to each. This article offers general suggestions only — always consult a licensed plumber before you alter any household plumbing.

Treated graywater#

Treated graywater generally carries lower health risks. Depending on the type of treatment, it can be used for a range of purposes, including garden watering, toilet flushing and in the laundry.

The drawback is cost: graywater treatment systems can be expensive to set up and operate, and in many places they must meet approval conditions set by the relevant authority before they can be used.

Untreated graywater#

Untreated graywater can be used in dry periods for gardens. You can do this by diverting it directly from your plumbing fixtures with a hose or diversion device, or by carrying it in a bucket. Depending on local rules, simple diversion of this kind may not need approval.

If it is not used properly, graywater can make household members ill and can damage the plants you are trying to care for. A few simple precautions will minimise the risks to you, your family and your garden.

Blackwater versus graywater#

‘Blackwater’ is water that has been in contact with toilet waste. It must be treated and disinfected before it can be reused. General precautions include:

• Never use water that has been in contact with a toilet, bidet or urinal.
• Don’t use water that has washed soiled nappies — this is also blackwater.
• Don’t reuse water used to wash pets, because of the high level of bacterial contamination.
• Don’t use graywater from the kitchen sink or dishwasher, as it can be contaminated with grease, bacteria and chemicals.

Common contaminants in graywater include bacteria and other disease-causing microbes, salts, food materials, soaps, detergents and household chemicals.

Comparing the health risks#

The risk depends on how you use untreated graywater. For example:

• Laundry rinse water is low risk, while kitchen graywater is high risk.
• Sub-surface irrigation pipes are low risk, while hosing the garden with untreated graywater is high risk.
• Using graywater on ornamental plants is low risk, while using it on vegetable gardens is high risk.

Setting up an irrigation system#

Several issues need to be considered before installing an irrigation system for untreated graywater:

• All household plumbing work must be carried out by a licensed plumber, so consult one before tapping into your plumbing system, and comply with the relevant plumbing standards.
• Your system should divert graywater from low-risk sources, such as the laundry rinse cycle, bath and shower.
• Your graywater must not leave the boundaries of your property, and must not discharge into any piped or surface drainage or stormwater system.
• Keep pipes away from underground agricultural pipes.
• Check how moist your soil is and spread the water around — don’t water the same spot every time.

Contaminants such as grease and slime can easily block pipes. A coarse filter may help avoid this. If you store graywater in a surge tank, keep it small (no more than about 80 litres) and fit an overflow drain that directs excess graywater straight to the sewer. A plumber can advise on installing a settling tank to capture grease.

Protecting your plants#

Some ingredients in cleaners and detergents can harm or kill plants, including total salts and sodium chloride. Check product labels carefully and choose products that are gentler on the garden.

Other suggestions:

• Use a coarse filter to reduce solids, otherwise your plants will suffer from clogged soil.
• Locate all irrigation below the soil surface; microbes from graywater survive longer on topsoil, so never hose, spray or mist untreated graywater.
• You may need to reduce the amount of fertiliser you use. Some native plants dislike extra nutrients, so plant selection can be important for managing nutrients and soil moisture.
• Water regularly with fresh water as well, to help prevent salts building up in the soil. Your local nursery can offer further advice.

Safe use in the garden#

• Use lower-risk sources of graywater, such as the shower, bath and laundry rinse cycle.
• Don’t use graywater on vegetable gardens.
• Don’t use graywater if any member of your household has gastroenteritis.
• Don’t irrigate in wet weather or when the soil is already sodden.
• Don’t let graywater form pools or ponds — microbes will thrive, creating bad smells and a health hazard.
• Don’t let pets drink graywater.

Reduce public access#

• Keep children away from garden areas irrigated with graywater.
• Make sure swimming pools, ponds and birdbaths are safe from graywater runoff.
• Encourage everyone to wash their hands before eating.

Improving the quality of your graywater#

You can improve graywater quality by managing how water is used in the first place:

• Choose phosphate-free or low-phosphate household cleaners.
• Install a lint filter in your washing machine.

Key points#

• There are health and environmental risks if you don’t use graywater safely.
• Treated graywater generally carries lower health risks.
• Graywater treatment systems can be expensive to set up and operate.
• A few simple precautions will minimise the risks to you, your family and your garden.
• Don’t reuse water used to wash pets, because of the high level of bacterial contamination.

Where to get help#