Essentially the effect is the same, but one reason is reducing conflict. A bidding war over water rights, for example, might mean that some regions don't get enough water to survive while others get enough to keep their golf courses green. Historically in the American West, that kind of thing has led to people dynamiting canals and so on.

A more balanced option might be setting a minimal delivery baseline for everyone in the watershed, with prices rising steeply above that baseline for the remaining water. This would encourage adoption of recycling, aka 'toilet-to-tap'...