Water will never become a valuable commodity for the foreseeable future (on a global scale). Most of the Earth's surface is covered by water, and we do very little that actually destroys water. What may become valuable is drinkable water, which is easily obtainable from sea-water (for the right price), an local access to water.
The first of these problems has an easy free market solution, and sets a hard cap on the value of drinkable water (as de-salination plants can scale linearly to meet our needs). The second of these is more difficult, but still has a worst case scenerio of needing to move people to water rich areas, and re-build infastructure to support the new population distribution, as well as dealing with a decrease in the habitable land area.
The first of these problems has an easy free market solution, and sets a hard cap on the value of drinkable water (as de-salination plants can scale linearly to meet our needs). The second of these is more difficult, but still has a worst case scenerio of needing to move people to water rich areas, and re-build infastructure to support the new population distribution, as well as dealing with a decrease in the habitable land area.