The water in the oceans and seas has many salts dissolved in it — the water is saline. So it is not fit for any agricultural, drinking or industrial purposes.
The process of changing of water into vapour and then returning to earth’s surface in the form of rain or snow is known as water cycle. And it is a continuous process.
Water vapour enters the air through the processes of evaporation and transpiration.
Evaporation of water is a slow process.
The process of condensation plays an important role in bringing water back to the surface of earth.
When the air moves up, it gets cooler and cooler. At sufficient heights, the air becomes so cool that the water vapour present in it condenses to form tiny drops of water called droplets. It is these tiny droplets that remain floating in air and appear to us as clouds.
When these droplets come together and get heavy, they fall as rain or snow.
Most of the water that falls on the land as rain and snow sooner or later goes back to the oceans.
Droughts cause wells and rivers to dry up, and it becomes difficult to get food and fodder.
The total amount of water on Earth remains the same, but, the water available for use is very limited and is decreasing with over usage.
Collecting rainwater and then storing it for future use is called rain water harvesting.
The basic idea behind rainwater harvesting is “Catch water where it falls”.
Rooftop rainwater harvesting is a technique where rain water collected in the roof tops is carried to a storage tank and then filtered to remove soil, and then it is directly flown in to the pit in the ground.