The issue is how to control it.
It is a classic resource allocation problem. How do you decide who could get access to how much of a limited resource? The options are:
1) Communist style central planning;
2) First come first serve;
3) Personal allowance + a price for consumption in excess of allowance;
1) and 2) lead to shortages and unfairness as the politically connected get unfair allocations.
3) forces users to decide if they really need the water on a case by case basis.
3) is by far the fairest system because each person can make the choice for themselves at a time when they need without some government official deciding for them or being forced to hoard water.