Water is a precious resource. We all know that it needs to be used more carefully in the future. Part of doing this is to recycle our household water.

Waste water that has been used for domestic use can be treated and recycled and made fit for use for irrigation purposes. Waste water should never be used raw or untreated, unless it very clean and there has been no contamination with human or animal urine or faeces, chemicals (oils, solvents) or heavy metals. The water can be treated in a number of ways, including filtering or use of settling ponds and constructed wetlands for removal of solids, biological treatment and disinfection.

There are two types of water that might be recycled from a home. These may be defined differently in different jurisdictions, but they are commonly referred to as: 

  • Grey water –Waste water generated from the bathroom, laundry or kitchen; and
  • Black water – Waste water from the toilet (contains urine and faeces).

Black water is not allowed to be reused without specialised treatment due to its high pathogen content. Its use is usually restricted to areas not linked up to a permanent sewerage system.


How can grey water be used?

By recycling our grey water we can reduce our water usage by around 30-50%.

Recycled water is generally used on the garden, although some states in Australia also allow grey water to be plumbed back to the laundry and toilet.

Its use in the garden will depend on:

  • What is in the water
  • How it is treated (if at all) after leaving the building
  • How it is applied to the garden
  • Where it is applied
  • Laws and regulations regarding its use.


What is in the water?

This will depend on both what you use it for and what chemicals (or other particles) are added to the water in the house.

Water that is used for washing people, clothes or dishes should be relatively clean provided that you have not added undesirable chemicals.


  • Detergents with high phosphorus
  • Detergents with high salt (less expensive detergent may use salt)
  • Disinfectants (eg. Bleach, Nappy wash)
  • Chemicals from household products such as toothpaste, mouthwash and shampoos.
  • Pesticides, Pharmaceuticals (Head lice treatment, Some pet wash chemicals)
  • Fats, grease, and oils from kitchen waste
  • Bacteria and viruses from soiled materials
  • Salinity (combined level of all soluble salts in the water) characteristics of water
  • Sodicity (level of sodium in the water) characteristics of water


Salt Levels and Interactions

Some salts are good for plants but others are not. The types of salts and relative amounts can be important.

If sodium is high, plant growth is inhibited and margins of the leaves can turn yellow and burn. High sodium only tends to be a problem when it is high relative to magnesium and calcium. Adding Dolomite (which contains calcium & magnesium) can correct this problem.

Adding phosphorus to the garden is not necessarily a big problem as it is useful for plant growth. Most plants benefit from addition of fertilizers high in nitrogen, phosphorus & potassium. If you are going to add phosphorus in waste water, you need to balance that by feeding plants with a fertilizer higher in nitrogen & potassium and lower in phosphorus.

Treated black water (eg. Coming from a Biocycle) may be higher in nitrogen than grey water. So again, you may need to balance this with the fertilizer you choose for the garden.


How is recycled water treated?

  • Filtration: particles, living or inorganic, are removed from the water with methods based on particle size using mesh.Items larger than the spaces in the mesh will be trapped, while smaller particles and water will drain through the mesh.
  • Biological Treatment: This is generally used to treat black water. There are various aerobic waste water treatment systems - such as Biocycle.This system separates and dissolves solid wastes, and treats waste water through a series of biological processes.
  • Chemical Treatment: Chlorination. Chlorine (Cl-) is added to the water. Chlorine is an effective oxidizer, thus modifying the living matter and killing potentially harmful organisms through oxidation.
  • Ozone treatment: Ozone (O3) is added to the water either as a chemical powder or liquid or bubbled into the water. Its high oxidative properties disinfect by oxidizing living matter. The principle is similar to chlorination but with oxygen instead.
  • UV treatment: This is the preferred method for biological and ecological systems, as no chemicals are actually added to the water. Bacteria are killed by the action of UV irradiation on them, as the UV light disrupts their genetic material (DNA). This method is not suitable unless the water is clear.Water must be clear for radiation to reach all the water and sanitation to be effective. This can be achieved by keeping water to be sanitised at a shallow depth.
  • Reed Beds: The use of reed beds is usually a secondary water purifying treatment. Aquatic plants are grown in a gravel-filled bed. As the grey water moves slowly through the reed bed, aeration and absorption of materials by plants improves quality of water.

A large range of aquatic plants are used in reed-beds, operating in different ways. Reed and rush species which are used for enriching the soil with oxygen include Phragmites australis, Phragmites communis, Schoenoplectus lacustris, Scirpus spp. and Typha latifolia (bullrush). These plants are the backbone of a good reed-bed system.

 Species which are suitable for pathogen removal include Alisma plantago-aquatica (water plantain), Juncus effusus, Iris pseudacorus (yellow flag), Mentha aquatica (water mint), Schoenoplectus lacustris and Spartina species. Cyanide compounds, thiocyanates and phenols have been removed using Juncus species.

Other plants which may be used in reed-bed systems include Carex spp., Eichornia crassipes (water hyacinth), Glyceria maxima (reed Sweet grass), Lemna spp. (duck weeds), Nymphaea spp. (water lilies), Pista sp. (water lettuce), Phalaris arundinacea (reed canary grass) and Symphytum officinale (comfrey). Many other species can be incorporated into the system depending on the locality and prevailing climatic conditions.

Planting trees which are tolerant of moist, nutrient-rich conditions (e.g. Allocasuarina, Casuarina and Melaleuca) adjacent to a reed-bed can further diversify the water treatment site.


How is recycled water applied to the garden?

Underground – Through a network of sub surface pipes (eg. Septic) or underground soaker hoses.

Surface – Drip system or soaker hoses.

Diverter systems – Non-treatment grey water diverter systems.

Surge tanks – Allows hot water to be collected & cooled before going onto plants.

Controlled Timing – Using holding tanks, using valves, timer, pumps etc…to apply at preferred times.Their use can be limited due to State Laws on holding grey water.

Ponds – Reed beds to clean water (may not be permitted in urban areas, permits may be required, some pre treatment of water may be necessary).




  • Use environmentally sensitive products in your household (e.g. shampoos, detergents).Check the labels for chemicals and excessive amounts of Phosphorous, Sodium and Nitrogen.
  • Rotate the area you irrigate to reduce the chance of toxin build ups.
  • Monitor the soil regularly – check the moisture level, pH, smell and signs of life in the soil such as worms.
  • Give your garden a break from grey water use from time to time.
  • Use a watering system that distributes water below the soil surface.
  • Mulch the soil as this will slow the penetration of toxins into the plant roots, giving them a chance to break down.
  • Check soil drainage.Undesirable microorganisms and toxins will be eliminated faster from the surface in a well-drained soil.
  • Check with your relevant Department of Health for current regulations.
  • Be aware of your local climate. The type and amount of rainfall you receive in your region can impact the effectiveness of grey water. If the area is flushed periodically (even if only seasonally), there is less chance of toxins building up over many years.



  • Don’t use on edible plants such as fruit trees or vegetables. Avoid applying any potentially contaminated waste water onto surfaces that will be eaten or touched (such as foliage of plants that could be touched, particularly by pets, children or wildlife).
  • Don’t allow grey water to leave the property.
  • Don’t irrigate during long wet periods.
  • Don’t use bleaches and disinfectants which will flow into the grey water untreated.
  • Don’t use sprinklers.
  • Don’t store untreated grey water for longer than 24 hours.
  • Don’t let untreated waste sit in a container where microorganisms and/or mosquitoes can breed.
  • Don’t let pets drink waste water.


Choosing Plants for Grey water

Some plants tolerate grey water better than others.Some plant groups that are known to tolerate grey water include:

  • Bird of Paradise
  • Melaleuca
  • Dietes
  • Gardenia
  • Callistemon
  • Conifers
  • Liriopes
  • Yuccas
  • Hibiscus

 Plant groups that do not tolerate grey water include:

  • Grevillea
  • Bougainvillea
  • Camellia
  • Lavender
  • Herbs
  • Ferns
  • Citrus
  • Azaleas


The Law

Local and State laws can vary regarding the use and application of grey water for private gardens.In most areas, home owners are allowed to use buckets and flexible hoses without permission. You may need to get permission from your local council before setting up a grey water irrigation system.It is advisable that you seek advice from your local council and state Health Department.

If doing pipe work or electrical work, it is likely that a plumber and/or electrician will be required in order to comply with local government regulations.

Black water may or may not be allowed to be re-used if treated (eg. through a biological treatment system).This may only be allowed in areas where there is no access to a permanent sewerage system.


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