In Australia, the average person uses about 138 litres of water every day. Given the amount of water we all use, it would be wise to try to recycle water as well as conserve it. Many people do not know that they can recycle much of their household water, known as grey water. As so much of household wastewater is grey, there is potential for half or more of a household’s total water use to be recycled.

Wastewater can be divided into two subgroups, grey and black water, depending on the amount and type of contamination in the water. Grey water is the wastewater that comes out of non-toilet plumbing systems. It usually leaves the household piping as soon as the water has been used and makes up a large proportion of the everyday household water use. Grey wastewater is from household activities like washing the dishes, doing the laundry and taking showers. In this water one can usually find organic debris, pathogens, bacteria and chemicals from cleaning products. Despite these contaminants, grey wastewater can be recycled for useful purposes.


Black water has a far higher level of bacteria than grey water, because it has a much higher concentration of organic matter and potentially dangerous bacteria like Escherichia coli (E. Coli). If any water is exposed to faecal materials or urine it will be regarded as black water, which cannot be recycled by a householder for further use. Black water needs to be properly treated in a sewage treatment plant.

However, people should know that they can use grey water on their lawns and gardens, unlike black water. The reason for this is because oxygenated water does not make room for decomposition. Disagreeable odours in the water are caused by septic decomposition, or anaerobic processes, that take place in the household systems. When grey water is used on lawns and gardens, the nutrients in the water are absorbed by the plants. The pathogens present are eaten by the naturally occurring micro-organisms in the soil, and other small animals like worms.

Neither grey water nor black water are suitable for human or animal consumption, however grey water can be used for some purposes including gardening. As mentioned, grey water has some level of microbial activity, but this is in nowhere near the levels in black water. The use of grey water for agricultural purposes helps in minimizing water usage, and it also helps in maintaining the natural balance of the environment.

To help prevent mixing of the two forms of water, it is important that households who want to use recycled water provide separate channels for two types of water. If this is not done and they are allowed to get mixed up, the grey water will be contaminated and unsuitable for recycling. If you do not know how to go about this, you can employ the services of a reputable plumber in your area to provide you with professional advice on how to proceed.