Aug 162010

Greywater is technically the household wastewater from the laundry (including the washing machine and tubs) and the bathroom (including showers, baths and basins). Toilet water and kitchen water are regarded as blackwater, and are not suitable for reuse in domestic gardens, due to the potentially high levels of bacteria, fats and solids contained in this wastewater.

The diversion of greywater from the house and into the garden has become an extremely popular way of irrigating our precious green spaces in these times of low rainfall and water restrictions, and, when done correctly, is an excellent way of saving water and money. It is amazing to think that one average household expels 830 000 litres of greywater a year! That’s more water than most gardens need in a lifetime! And, unlike rainwater, greywater is available all year round, regardless of the weather!

Recycling household greywater for use on garden beds is an excellent way of saving water and saving money! Unlike rainwater, which is seasonally available, greywater is available every time you shower or wash. The average house creates up to 83,000 litres of greywater per year.

Using greywater in the garden
Greywater is suitable for irrigating most garden areas including ornamental beds and lawns. Even native gardens can thrive with greywater, simply alter the type of detergent that you use to one that is low or has no phosphorus. It is recommended to always check on the plants and the soil that is being irrigated with the greywater. If you do notice any negative effects on the soil or the pants, change the watering regime or rest the area from grey water use for a period of time until the plants return to a higher level of vitality.

Will a system work at my house?
There are several ways to set up a greywater system, which may depend on the amount of ‘drop’ from the greywater origin to the garden bed. Systems can be as simple as a flow diversion fitting and hose, or something more complex such as a holding tank and pump with underground agipipe irrigation.

Are there components of greywater that can affect my garden?
As a general rule it is best to avoid irrigating gardens when the following are in your greywater:

  • Washing detergents with high phosphorous levels (many brands now have low or nil phosphorous, so choose one of these)
  • Bleaches and other disinfectants
  • Fats (from soaps)
  • Washing detergents using salt. Many cheaper brands use salt as a filler. It does not add to the washing power of the powder. Use only concentrates; or, better still, liquid detergents.

For a comprehensive list of detergents and the levels of salt and phosphorus that each contains please visit

How will my plants respond to Grey Water?

Most plants thrive with the application of greywater, but there are some exceptions. Greywater contains a range of chemicals that can become toxic if the water is not used correctly. Greywater is normally alkaline due to the detergents in the water, it may also contain high levels of salt and phosphorus. Below we examine how each of these elements react with your plants, how to diagnose that there is a problem and what to do about it.


Most Laundry powders create alkaline (high pH) wastewater, pH affects the availability of certain elements that plants require to survive. One of the major elements effected is iron, iron availability decreases as alkalinity (pH) increases.

Symptoms of a deficiency in available iron for a plant include the younger leaves becoming a lighter green or almost white but the veins remaining darker green. (see picture on the right) Acid loving plants are poor at obtaining iron hence their requirements for low pH soils. These plants include: Azaleas, Camellias, Gardenias, Rhododendrons, Begonias, Ferns, Hydrangeas, Impatiens, Magnolias, Primroses, and Violas. Alternating between greywater and alternative water sources helps to maintain pH at suitable levels. If further reductions in pH are required the addition of Sulphate of Iron will assist with both problems. In most cases high levels of organic matter in the soil help buffer any effects on pH that the addition of greywater may have.


The levels of phosphorus in the soil may increase depending on the type of laundry power used. Signs of Phosphorus toxicity include necrosis (browning and death) of tips and margins of older leaves followed by dropping off of the affected leaves. Chlorosis (yellowing) of younger foliage often occurs and the plant dies in severe cases. Phosphorus toxicity is rare in many species but there a small number of species that are most prone to the problem. Of these species the majority are Australian natives from the Proteaceae family.

Some Phosphorus sensitive species include Acacia baileyana, A.iteaphylla, A.obtusata, A.sauveolens, A.verticillata, Banksia aemula, B.ericifolia, B.oblongifolia, B.robur, Beaufortia squarrose, Boronia megastigma, Callistemon citrinus, Grevillea aquifolium, G.glabella, G.“Poorinda Firebird”, Hakea laurina, Protea longifolia, P.macrocephala, Pultenaea pedunculataa and Telopea speciosissima.

Even if your garden does not contain any species that are vulnerable to high levels of phosphorus please consider the effects that the phosphorus will have if it reaches the natural environment. Higher levels of phosphorus in our river systems contribute to Blue-green algal blooms (see picture on the right) that are toxic and damaging to river health. Native ecosystems quite vulnerable to any changes in nutrient levels and harmful to many native plants.

Salt is found in many of the cheaper detergents as filler for bulking out the product. These salts are harmful to plants. Certain species are less tolerant to salt than others but in high concentrations salt is fatal all plants. Symptoms of salt damage include slow or no growth, necrosis (burning and dieback) of young growth and dead and brown sections on the margins and tips of older leaves. (see picture on the left) If you notice salts rising to the surface or the plants showing signs of salt stress replace the use of greywater with an alternative water source and change the type of laundry power that you are using to one that contains less salt.

What will greywater do to my soil?
Hard to say really! As we have learnt, the use of greywater with a high content of laundry detergent can be quite harmful to plants, causing phosphorus toxicity and sodium issues. But the truth is, we don’t know at this stage what the long term impact of greywater use on gardens will be. The widespread use of greywater for irrigation is a fairly new beast, and one that, until now, has not been studied a great deal. While there are numerous studies underway, the outcome on soil health will not be known for some time. But we can infer a few things at this stage:

  • The use of harsh chemicals that are designed to kill household bugs are most likely to kill beneficial bugs in the soil. This includes the use of eucalyptus oil, nappy soakers, antiseptic and anti-bacterial products, and carbolic acid based disinfectants.
  • Petroleum based products such as some detergents and optical brighteners – they are slow to bio-degrade, and probably not real good for the soil

Maintaining soil health by adding plenty of organic matter is essential (even more than usual) to counteract the effects of any additional salt. It will also help to buffer the pH because another benefit of adding lots of organic matter is that it can help lower pH, which in turns makes less phosphorous available to plants. Check out the soil health section of our website for more information on the importance of healthy soils!

Are there any health issues related to greywater use?
Again, there are situations where greywater can contain organisms that may pose health concerns, however this can be avoided by following these points:

  • Don’t use nappy-wash water in greywater
  • Don’t allow children to play with or in the greywater
  • Don’t allow pets to drink the greywater
  • Use subsurface distribution such as porous hoses or drippers beneath a layer of mulch -that is, do not spray greywater into the air
  • If irrigating edible plants, don’t use on plants that are consumed raw or undercooked. Preferably don’t use it on food crops at all. Fruit trees can be irrigated with grey water but the water must be kept at the root zone and not sprayed onto the foliage or fruit.
  • If holding tanks are used, don’t store unused greywater for longer than 24 hours and remember to keep filters on tanks free of lint. Tanks must be cleaned out regularly to remove sludge build-up

Plumbing regulations state that drainage and water supply work must be carried out by a licensed plumber. This includes plumbing greywater overflow back into the sewage system. Refer to the EPA in your state and your local council for laws governing the use of greywater in your area.

Simple diverter systems
The simplest way to get water greywater onto the garden is by diverting the water directly from the laundry or bathroom. There are a number of products available on the market that range in price depending on their complexity.

Funnel inserts
One of the simplest products, the black rubber funnel is ideal for situations where the water does not need to be diverted away quickly such as from a bath. This style of device does not need to be installed by a plumber and is easily removed when not required. Simply unscrew your wastewater inspection cap and insert the funnel.

This system is prone to backflow due to the narrow opening on the black funnel. To avoid flooding, thoroughly test this option by remaining present while it is active.

In-line diverter
In line diverters are designed to cut into the existing wastewater piping from the bathroom or laundry. Most systems rely on a valve that allows the water to either be diverted onto the garden or continue on down to the sewage.

Make sure that the water from toilets or the kitchen are not able to flow into the diverter, check the location of all piping prior to installing the diverter.

Dispersing the water
All piping must remain below the height of the diverter and must also be able to be dispersed from the system as quickly as it enters so that the water will not flow straight back into the house. Using 50 mm or 65 mm drainage (Agi.) pipe decreases the chance of backflow problems. Simply join some un-slotted drainage pipe to the diverter with a 3-4 m section of slotted drainage pipe on the other end, run the pipe to the area that you want to water and lay the pipe out running with the slope of the land.

Diverters incorporating surge tanks

Using a surge tank in a greywater system allows water to be slowed and cooled before it reaches the garden. Backflow problems are far less common as an overflow on the surge tank sends any excess water down the sewer rather than back into the house.

Water distribution is more consistent over the entire length of area irrigated. Decreasing the speed in which the water travels to the garden helps to minimise water runoff and prevents mulch and soil from washing away.

The Surge tank
Water from the bathroom or laundry enters the top of the surge tank via a pipe no smaller in diameter than that coming out of the house. Located at the base of the tank is the pipe that carries the water to the garden. An overflow from the tank is located at the top of the tank that flows back into the sewer, this pipe should be the same diameter as the inlet pipe.

A tank size between 30 and 100 litres is normally adequate as a surge tank for the majority of applications.

Greywater cannot be stored for any longer than 24 hours, always ensure that all water has drained completely from the tank at the end of each cycle.

Dispersing the water
The water is best distributed in pipes laid between the soil and mulch layer, piping options include drainage (agi.) pipe, standard poly pipe with holes drilled and dripline. The choice of piping depends on the size of the filter used.

The finer the filter, the more maintenance required, systems with filters and low water emitting drippers are more likely to get clogged by hair and lint. Where possible try not to use filters at all.

Pumped Greywater systems
Pumped greywater systems allow the water to be pumped from a lower to a higher section of the property. This is necessary when the garden is located above the height of the house. Pumped systems usually include some type surge tank where the pump is located and require power to operate.

Pumped systems require electricity, a licensed electrician may be necessary to install an outdoor electrical outlet. Pumped systems normally require a number of filters that require maintenance to prevent foreign objects from blocking the pump.

Dispersing the water
All pumped wastewater must be dispersed underground. A hose connected to the pump is normally placed at the highest end of the garden bed to be watered. The hose is inserted into 50 mm drainage (agi) pipe located between the mulch and soil surface running down the length of the bed. Moving the hose between garden beds every 2-3 days ensures even watering across the entire property.

Bulleen Art & Garden employ the services of experienced greywater consultants who can advise you at your home on the installation and suitability of a greywater system for your garden. Greywater systems are very site dependent. Our consultant will leave you with knowledgeable advice, a rough plan, discount vouchers and relevant handouts. Please see the consultants section of the website for bookings and costs.

Many of the greywater systems require a plumber to install them. At Bulleen Art & Garden we can arrange for an experienced tradesperson to come and install the system for you. Please see the reliable tradesperson section of the website for bookings.