Rainwater is a free gift of nature and it can be collected easily in small and large quantities by various methods and for various purposes. Harvesting rainwater involves gathering and preserving water from rain before it reaches the wet underground layer of the earth that contains permeable rocks and unconsolidated materials.

In under-developed parts of the world where pure drinking water is not readily available, they adopt the option of gathering water from the roof of their houses. They sometimes process this water mildly, most times by boiling, and then consume it and drinking water and also to cook. The materials used for collecting the rain water are readily available in their local communities. They however, have to cope with the challenge of rainwater storage systems as the rain does not fall all through the year.

Harvesting rainwater can also be done on a larger and more advanced scale. This usually involves using a complex industrial system, such as the below ground tank, which is often regarded as the best option for gathering rain water. The tank traps and preserves subsurface water. A simple calculation can be done to determine how much water and at what rate it can be gathered, by applying a little arithmetic calculation to some parameters.

The advantages of gathering rain-water for use is that there is no reliance on any systemic supply source. There are no restrictions to usage and it is quite appropriate for a few domestic needs. It is also renewable and at varying but considerable volumes.

Rainwater gathering presents one major disadvantage, besides the fact that it can be slightly unpredictable, it is highly exposed to contaminants and pollutants. Those who rely on rain water for general assistance stand a very good chance of falling ill often. Except they adopt proficient ways to purify the water and make it safe for consumption and domestic use. For those in the urban area this is not a problem, they have several water supply options and also have adequate water treatment systems to purify gathered rain water. However, those in the rural areas lack suitable ways to purify the water and so they are prone to many water-borne diseases.