Water harvesting is the activity of direct collection of rain water. The rainwater collected can be stored for direct use or can be re-charged into the ground water.
Rain is first from of water that we know in the hydrological cycle, hence it is a primary source of water for us. Rivers, lakes and ground water are all secondary source of water.
In the process , it is forgotten that rain is the fundamental source that feeds all these secondary source.
Water harvesting is a concept to understand the value of rain and to make optimum use of the rainwater at place where it falls.