The water on earth surface constitutes hydrosphere. About 75% of earth surface is covered with water and 97% of that water is present in oceans, which is very salty.
We are only left with 3% of water, out of which considerable amount is locked in icy mountain caps and only 0.3% of water present in hydrosphere is available for human use. There is continues circulation of water between hydrosphere and water vapor in atmosphere by natural water cycle.