Rainwater harvesting is the accumulating and storing of rainwater for reuse before it reaches the aquifer. It has been used to provide drinking water, water for livestock, water for irrigation, as well as other typical uses. Rainwater collected from the roofs of houses and local institutions can make an important contribution to the availability of drinking water. It can supplement the subsoil water level and increase urban greenery. Water collected from the ground, sometimes from areas that are especially prepared for this purpose, is called Stormwater harvesting. In some cases, rainwater may be the only available, or economical, water source. Rainwater harvesting systems can be simple to construct from inexpensive local materials, and are potentially successful in most habitable locations. Roof rainwater may not be potable and may require treatment before consumption. As rainwater rushes from your roof it may carry pollutants, such as mercury from coal burning buildings, or bird faeces. Although some rooftop materials may produce rainwater that would be harmful to human health as drinking water, it can be useful in flushing toilets, washing clothes, watering the garden, and washing cars; these uses alone have the amount of water used by a typical home. Household rainfall catchment systems are appropriate in areas with an average rainfall greater than 200 mm (7.9 in) per year, and no other accessible water sources (Skinner and Cotton, 1992). Overflow from rainwater harvesting tank systems can be used to refill aquifers in a process called groundwater recharge; though this is a related process, it must not be confused with rainwater harvesting.

There are several types of systems to harvest rainwater, ranging from very simple home systems to complex industrial systems. The rate at which water can be collected from either system is dependent on the plan area of the system, its efficiency, and the intensity of rainfall (i.e., annual precipitation (mm per annum) x square meter of catchment area = litres per annum yield) ... a 200 square meter roof catchment catching 1,000mm PA yields 200 kLPA.

ld be large enough to carry peak flows. Storage tanks should be covered to prevent mosquito breeding and to reduce evaporation losses, contamination and algal growth.

A subsurface dike is built in an aquifer to obstruct the natural flow of groundwater, thereby raising the groundwater level and increasing the amount of water stored in the aquifer. The subsurface dike at Krishi Vigyan Kendra Kannur under Kerala Agricultural University with the support of ICAR, has become an effective method for ground water conservation by means of rain water harvesting technologies. The subsurface dike has been demonstrated to be a feasible method for conserving and exploiting the groundwater resources of the Kerala state of India. The dike is now the largest rainwater harvesting system in that region.

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• Texas Water Development Board- Rainwater Harvesting
  twdb.state.tx.us
  Links to the Texas Guide to Rainwater Harvesting and to equipment and services providers.
• Domestic Rainwater Harvesting
  lboro.ac.uk
  This fact sheet gives an overview of systems, component technology, planning and management, as well as the potential effects and impacts.
• Rain Barrel Information and Sources
  kingcounty.gov
  Features information and resources on systems for collecting rain water.