Which  one of following is not a reason for shortage of usable water?

Overuse of the water resources will result in the exhaustion of the water supply. The climatic change has resulted in global warming and seasonal variations. There is a decrease in the annual rainfall which was received by a region due to shortening of the seasons. Deforestation has resulted in a decrease in the number of trees which thereby affect the amount of rainfall which was received. There is soil erosion which results in water run off.The decrease in the level of the sea is not a reason for the shortage of usable water.