It is because the natural pace of recycling the water through Earth's systems is too low as compared to the current pace of its utilization.
This is the reason that environmentalists consider freshwater as nonrenewable.
The current rate of water pollution has decreased the world's supply of freshwater. The most prominent decrease can be observed in South America, North America, and Asia.
The freshwater will be depleted completely soon if we keep exploiting it in an unsustainable manner.
