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Greywater

Greywater is waste water derived from household appliances; which includes water from the shower, dishwasher, bath, sink, and washing machine. Instead of this water being wasted down the drain, greywater can be re-used for all the household needs and other needs such as watering the garden, flushing the toilet and washing the car. Incorporating a greywater system within your home will provide significant savings through reducing your water consumption, ultimately reducing your water bills, (a particular concern if you are on a meter). A well designed greywater system could potentially save a third of water used throughout the home.

It should be noted that “greywater re-use” is the use of untreated greywater and “greywater Recycling” is the use of treated greywater.

Whitewater, Greywater and Blackwater

The differences between these three are simply the colour of the water and the amount of chemical and biological contamination contained within the water. White water is drinking water and is clear with no contamination, or harmful chemicals. Greywater is grey with few chemicals or contaminations and blackwater is water from toilets or sewage. Blackwater contains a lot of chemicals and is highly contaminated.

Types of Greywater Systems

Greywater systems vary in size, complexity and cost; here is a list of the different systems:

Direct re-use systems – these very simple systems use greywater without treating it, which is acceptable as long as the greywater is not stored for a long time before use. This system can utilise bath or shower water, which as soon as it’s cooled, can be used to water the garden or for an array of alternative purposes. This can be achieved by installing a valve to the external waste pipe that takes water from the bath to a water butt.

Short retention systems – This type of system applies a very basic treatment to the greywater, such as skimming the top of the water and letting any debris and particles sink to the bottom of the tank; this is a cheap system with low maintenance.

Basic physical and chemical system – This system filters the water to remove debris before storage, while disinfectants are used to stop bacterial growth. These systems can be quite unreliable according to several studies, although they did provide saving on water consumption.

Biological systems – In these systems bacteria is used to remove organic material from the wastewater. Oxygen is added to the wastewater so the bacteria can digest the contamination, which is the same system used in sewage works. The Oxygen can be introduced to the wastewater in several ways, oxygen can be pumped into the water using a pump similar to a small fish tank or plants can be used to add oxygen to the water.

Bio-mechanical system – This system is the most complex and combines most of the techniques described above. Solid materials are allowed to sink to the bottom of the tank, oxygen is added to the water, along with filtering and UV disinfection.

Don’t forget that the less the water has been treated the less time the water can be stored before use.

Before Considering Greywater

  • While simple greywater systems provide some clear benefits, more complex counterparts have many trade-offs such as energy use and space.
  • The reliability of greywater systems is unproven and maintenance costs are speculative.
  • It’s usually better to install greywater systems while doing some other upgrade or refurbishment to your home, rather than just installing a greywater systems individually, largely because of the cost.
  • Greywater systems incur long payback times, due to the local water charges and the demand for non-potable water.
  • A community greywater system would provide increased water quality, be more reliable and provide better cost savings, so community systems would be better than individual systems.
  • Greywater systems don’t necessarily save energy, they save fresh water usage. To save energy it would be better to concentrate on water efficiency and saving the amount of hot water used throughout the home.