A rainwater catchment is a container which is designed to hold rainwater. Reclaiming rainwater instead of letting it drain away is a practice common in several regions of the world and something which humans have been doing for centuries. Originally, people harvested rainwater because they had limited water supplies, and didn't want to let gifts from the sky go to waste. As people became more aware of ecological issues, some communities began adopting rainwater harvesting to reduce their burden on the environment.
There are several ways in which a rainwater catchment can be used. One of the most basic systems is a tank attached to a home. Gutters on the home capture rainwater and route it into the tank when it rains. The tank may be attached to a pump which can be used to pump out water, or it may be set up to create a gravity feed system which requires no electricity. Such systems can be used to supplement water needs for a home, or to fully meet them, depending on the area.
Home systems may utilize underground tanks or above ground tanks. The advantage of tanks above ground is that they can be used with a gravity feed system to ensure that people can access water when there is no electrical power. The major drawback to an above ground rainwater catchment, however, is that a large tank of water is not terribly attractive, and there isn't much that can be done to conceal it. In some communities, people may be required to bury catchment tanks for aesthetic reasons.
Communities may use a different type of rainwater catchment system, in the form of a large underground tank in the middle of a sloped area which has been prepared to trap water. When it rains, water flows down the slope and into the tank. This system works well in areas where a communal water source may be useful. A ground catchment can also be linked with several similar catchments to create a large reserve of water.
Rainwater is not necessarily safe to drink. Water collected in a rainwater catchment may be suitable for things like gardening, flushing the toilet, and some cleaning tasks, but it will need to be purified before it can be consumed safely. Purification systems vary in cost and complexity, with several companies manufacturing very basic systems which can be used in communities where people may lack resources to buy or maintain a sophisticated system.