The hydrosphere is the total amount of water on the planet. The amount of water in within the global water supply is 1385000000km3 and, whilst less than 3% of this is fresh water, this is still far greater than current population requirements. Water also exists in various forms, ranging from dew to ice.
The Water Cycle
Ways in which human activities affect rivers include:
Changes to Seasonal Flaws
Reduced River Flow
Disruptions to migratory patterns