Rainwater Harvesting

Rainwater harvesting is simply collecting rain which falls onto roofs, then storing it and using it as a free resource.

The advantages of rainwater harvesting are that it,

»    Saves money by reducing your water usage,
»    A volume of water is kept out of the storm-water management system, thus helping to reduce flooding risks,

»    Gains Eco-homes rating points for your property,
»    And rainwater is better for your garden as it has a balanced ph and is free of chemicals such as chlorine.

If it is correctly collected and stored, rainwater can be used for toilets, washing machines and watering gardens without further treatment. In practice, most domestic roof areas are too small to satisfy all this potential demand regardless of the size of the storage cistern, so it is important to evaluate the potential savings before investing in an expensive installation.

Rainwater Harvesting Systems can be very simple such as a water butt located under a down pipe from your guttering that you use to fill a watering can or connect to an inexpensive syphon hose to water your garden.

The garden water butt is the simplest way of collecting rainwater. It does not need any treatment or mains backup, and it does not have to supply water when temperatures are below freezing. Household rainwater systems are, however, much more sophisticated and their installation is quite complex.

At the other end of the scale these systems have large above or underground tanks, filters and pumps which will not only feed to your garden irrigation and car wash but also into all the non-potable uses inside your home such as toilets, washing machines and even showers and baths.

Some of the larger systems even have PV panels to generate the power to drive the pumping and water management systems that ensure that the system is topped up by mains water when rainwater is scarce.

These systems can be subdivided into two types; Header Tank Systems and Direct Pump Systems.

Header Tank Systems as the name suggests require a header tank to be installed in the loft, have a high reliability, can easily revert to mains supply if rainwater is scarce and the control system is simple and inexpensive. However the pressure may be too low for some washing machines and flush toilets may take a while to fill.

The majority of commercially available systems are Direct Pump Systems that do not require a loft tank and generate a good pressure suitable for washing machines that are used to the pressure from a direct mains feed and suitable for car wash equipment and garden hoses. However, the control mechanism is likely to be more complex (and expensive).

The Environment Agency's Water Resources section has a useful overview of Rainwater Harvesting.

http://www.environment-agency.gov.uk/homeandleisure/drought/38559.aspx