Last edited 13 May 2019

Greywater recycling

Water is an increasingly scarce resource. As population increases, and climate change makes rainwater patterns less predictable, it is becoming more important that we reduce the amount of water that we consume and discharge into the sewerage infrastructure.

In addition, the treatment of water to make it suitable for drinking and other uses consumes a considerable amount of energy. Treating water to make it suitable for drinking just to use it for purposes that do not require this level of treatment, such as watering gardens or flushing toilets, is extremely wasteful.

Environmental concerns, utilities bills and the imposition of restrictions such as requirements for sustainable urban drainage systems and hosepipe bans means that people are increasingly looking to re-use or re-cycle water.

Typically water is categorised within one of three broad groups, with the degree of contamination increasing and so the number of suitable uses decreasing and the treatment requirement increasing:

Fresh, potable water or ‘drinking water’ is sometimes referred to as ‘white water’.
Wastewater from showers, baths, washbasins and washing machines that is not considered to be potentially dangerous, is referred to as ‘greywater’.
Water from toilets that may be contaminated with hazardous material is referred to as ‘blackwater’ (or sometimes brown water, foul water, or sewage). Some definitions of blackwater also include water from kitchen sinks, dishwashers and waste disposal units which may contain food particles.

It is possible to collect greywater and, after treatment, use it for purposes that do not require drinking water quality, such as toilet flushing and garden watering. This greatly reduces the demand on mains water as well as reducing the volume of water discharged into sewage systems.

As well as conserving water this will also save users money on their water bills (if they have water metres installed). According to the Environmental Agency (2011), greywater recycling systems have the potential to reduce the amount of mains water used in the home by about a third.

The limitations of initiatives such as rainwater harvesting and greywater harvesting are that even though it reduces demand for mains water, it does not actually contribute to a reduction in water consumption. In addition, long payback times combined with small storage volumes mean it can be less effective than other water conservation measures.