Currently here are significant pressures on mains water supplies affecting much of England south of the Humber estuary, in particular the south-east region; these pressures are predicted to increase over future decades due to a combination climate-change impacts on weather patterns over the UK, and a growing population.  Government and others are therefore reviewing their policies and plans to mitigate these pressures and help to ensure the continued availability of sufficient water to meet the needs of people, the natural environment, industry and commerce.

Water reuse systems such as rainwater harvesting can play a very useful role in helping to ease the pressures on mains water supplies by using the rainwater collected for domestic purposes such as toilet flushing, use in clothes washing machines, or to feed outside taps.  Typically, using harvested rainwater will reduce the quantity of mains water used in the home by around 40%.  Used in suitable commercial premises this saving can increase closer to 80% in any building that combines a large collection area, which is usually the roof, with a high demand for the water collected.


Typically, rainwater harvesting systems are best used in buildings that have sufficient roof area to meet the non-potable water requirements of their occupants.  In high-density buildings with a low roof area to occupancy ratio, such as hotels and hostels for example, this limitation can be overcome by switching to greywater recycling technology which collects and treats shower and bath waste water to produce the non-potable water needed to flush toilets.

Although greywater recycling systems are more complex and costly than their rainwater harvesting counterparts, they are nevertheless cost-effective due to the good match between the mains water needed for bathing purposes, and the quantity of recycled water needed to flush toilets.  In major projects, both technologies are often used in conjunction to achieve maximum savings on the use of mains-water.

Rainwater harvesting and greywater recycling systems are bespoke to the application for which they are designed.  They therefore vary widely in their specific designs, so the descriptions of each, accessed via the icons below, are generalised to explain in basic terms how the systems work.