Why is water harvesting so important?

Water is said to be the elixir of human life. It is a prime natural resource, a basic human need and a precious natural asset. Over the years due to increase in population, irrigation and industrialisation, the demand of water has gone up to a large extent. This has lead to scarcity of water to such a level that it is being said that the third world war will be caused over the issue of water. Therefore water harvesting is important.