Rainwater harvesting is a form of greywater and it refers to gathering the rain which would otherwise flow from a roof and into a drain, and using it instead to flush toilets, wash cars, flush toilets and so forth – rather than using drinking water.
There are different rainwater harvest systems available. Most will involve having a storage tank fitted to the drain from your roof. The rainfall will enter the tank via a filter, which will remove leaves and any other organic matter. The tank will generally be buried to save space – often under car parks, gardens, or under a drive. It will have a pump to transport the rainwater into the building for onward use.
These systems are useful in domestic properties, as well as for schools, offices, hospitals, commercial premises and other building types where water is needed for cleaning, flushing toilets or watering gardens. Some buildings will even use greywater for certain types of washing machines or commercial ‘pre’ washes.
A rainwater harvest system can make a saving of up to 30-50pc of treated drinking water within domestic properties. For commercial buildings, the savings can be higher and as much as 80pc. A corresponding drop in water bills can usually be noted and being on a water meter is the best way to benefit from this cost saving.
Typical rainwater collection volumes will depend on the collection area, the angle of your roof and the area that you live in, however, a typical average for a household system is 100,000 litres and commercial buildings with large roofs may collect far more.
A domestic system will typically cost anything from £2,500 upwards, including the cost of the tank and installation. Commercial systems will cost more, but tend to have a more rapid payback period. Currently, there are no grants available for domestic installations, but a range of environmental organisations are putting their case to the government, for grant assistance.