Rainwater harvesting is a technique of collection and storage of rainwater into natural reservoirs or tanks, before it is lost as surface runoff. The harvesting of rainwater simply involves the collection of water from surfaces on which rain falls, and subsequently storing this water for later use. Normally water is collected from the roofs of buildings and stored in rainwater tanks. Not only does this recharging arrest groundwater depletion, it also raises the declining water table and can help augment water supply. Rainwater harvesting and artificial recharging are becoming very important issues. It is essential to stop the decline in groundwater levels, arrest sea-water ingress, i.e. prevent sea-water from moving landward, and conserve surface water run-off during the rainy season. Rainwater Collection Rainwater collection systems were widely used before well drilling equipment and treated municipal water supplies became available. In many parts of the world, rainwater still provides the majority of the water needed to meet agricultural requirements and, in some cases, potable water as well. Most rainwater collection systems are designed to capture rainwater from the roofs of buildings. The water is then transported through catchments and other pipes into tanks, where it is stored until needed. The water collected can be used for irrigation, laundry, hygiene, or even potable water, depending upon the materials used and the treatment undertaken by the homeowner. A typical rainwater collection system consists of the following: A collection area (usually the roof) A method of conveying the water (gutters, downspouts, and piping) A filtering device usually sand filter A storage tank or cistern A system to distribute the water as needed Provided the rainwater is for non-drinking water purposes, virtually any materials can be used in the collection system. However, if the rainwater will also be used to meet the potable water needs of a home's residents, it is important that the homeowner use care in selecting materials and coatings which will come into contact with the water as it is collected, since some impurities can be picked up by the rainwater as it travels through the collection system. There are several options when it comes to selecting a storage container for the water. Most storage tanks or cisterns are constructed from concrete or fiberglass and can be located either above ground or below. If you do plan to use the collected rainwater for drinking, make sure the materials and/or coatings used in the construction of the storage reservoir have been tested to ensure they do not leach harmful contaminants into the water being stored. Regular microbiological testing should be performed on all non-municipal drinking water supplies to ensure the water does not contain any harmful forms of bacteria.