Understanding greywater

What is greywater and why use it?

All the water that comes out of the tap is top quality drinking water, but not all of the activities around the house need drinkable water. Greywater is the used water from the bathroom, laundry and kitchen. It doesn’t include water from the kitchen sink or from toilets (this is known as black water).

Greywater can be a great option for your garden watering because most people have a plentiful supply, it doesn’t rely on rainfall or vary much with seasons and it reduces your reliance on potable (drinking quality) water. It can also be used for flushing toilets. 

It's important to seek professional advice though before you implement grey water though; it may contain disease-causing organisms and if you don't manage it properly it can be hazardous. The general advice is not to store greywater for any length of time but to use it immediately for its purpose, ie: put it straight on the garden.

Using greywater on your garden

You can re-use water from your shower and washing machine... but use it last. This means when looking for water to put on the garden, start with the water you rinse your veggies in, then bath and shower water, then laundry rinse water and if you still have areas that need water, use your laundry wash water last and add it to the garden below ground or under mulch. 

This is because bath, shower and laundry water contains some bacteria, detergents, cleaning agents and waste material, so it isn’t suitable for all garden uses. 

Like most things, what you get out of greywater depends on what you put in. Gardens are living things and the chemicals and bacteria we add to greywater can have short and long effects on your garden and your health. Fortunately most impacts can be addressed by being careful about what you add to greywater and being careful about how you store, treat and use greywater.

One of the potential impacts of greywater is increasing salt content. This has a long term impact on the soil structure in your garden and can be very difficult to fix later on. Common sense tells us to avoid concentrating greywater in one area of your garden, avoid putting too much on and monitor the health of your plants and the state of the soil where you use greywater.

Having given you the warnings many gardeners have really enjoyed being able to recycle their home water in such a rewarding way. A little seaweed solution added in with greywater can act as a gentle fertilizer. You might also note that the phosphates in most soaps will not be appreciated by your native plants but the lawn usually loves them!

Other uses for Greywater

These generally relate to treated greywater and include industrial uses, washing vehicles, flushing toilets and other uses that do not require high quality water.

Working safely with greywater

There are a number of do's and don’ts to be taken into account when installing and using a greywater system. These vary depending on the type of system used and the level of treatment.

Greywater Diversion Systems (Untreated greywater)

  • DO use a licensed plumber to install the diversion system
  • DO use low risk sources for water diversion systems such as bath, shower and laundry rinse water (Laundry wash water is much higher in detergent concentrations than rinse water);
  • DO be aware of biodegradable labelled products (e.g. soaps and detergents). Liquid based products are generally better (check the ingredients on the packaging);
  • DO only divert greywater in dry conditions, in quantities that can be taken up by plants & soil (i.e. avoid over irrigation and runoff); and
  • DO apply with buckets or watering can onto garden or use subsurface garden irrigation only (to council setback requirements). 
  • DON’T use untreated greywater from the washing of nappies or soiled clothing.
  • DON’T use untreated greywater when a resident has diarrhoea or is sick.
  • DON’T use untreated greywater generated by cleaning in the laundry or bathroom, or when using hair dye or other chemicals.
  • DON’T use untreated greywater generated by washing rags used for painting or for maintaining machinery.
  • DON’T store untreated greywater for more than 24 hours, as it illegal in most states.
  • DON’T use kitchen water for greywater as it is heavily contaminated with fats, greases and solids.
  • DON’T apply untreated greywater to vegetable gardens.
  • DON’T over water with greywater (any water) as it can raise the local water table or cause excess to run off into other properties or waterways.
  • DON’T use water from toilets for greywater.

Greywater Treatment Systems (Treated greywater) 

 When installing a greywater treatment system and using treated greywater:

  • DO select garden-friendly detergents that are biodegradable and low in phosphorus, sodium, boron and chloride (select liquid washing detergents, as they are comparatively low in salts).
  • DO monitor plant and soil response to treated greywater irrigation.
  • DO ensure that regular maintenance of the treated greywater system is undertaken.
  • DON’T irrigate with treated greywater during rain.
  • DON’T use treated greywater to top up rainwater tanks or swimming pools;
  • DON’T irrigate with greywater if the premise is located on an aquifer that is used for drinking water;
  • DON’T use treated greywater on plants that will be eaten raw or where fruit has fallen to the ground;
  • DON’T use treated greywater so that it flows into the streets or down stormwater drains; and
  • DON’T let treated greywater go beyond the premise and cause a nuisance to neighbours
  • DON’T use water from the kitchen, handbasins or toilets for treated greywater

Discover more about using greywater:

 

Using greywater

 

Greywater diversion systems

 

Watering with greywater