Not that I'm the first to foresee a future where water is added to the mix of natural resource wars, but this article in Reuters discussing potential water rationing in Los Angeles certainly hints at a future where obtaining water will require more then simply turning on the faucet.
In making such a statement I was pointed to a film which prophesied an apocalyptic water influenced Earth long before Kevin Costnar grew gills. The film is The Ice Pirates, which takes place in a future where water is an immensely valuable substance, both as a commodity and as a currency. Princess Karina is a spoiled princess who purchases captured space pirates. They then proceed to locate a "lost" planet that contains massive amounts of water.
The movie looks ridiculous, and meant to be tongue and cheek, but the core story line which might of seemed far fetched in 84' doesn't appear to be so much now. We have alternatives for oil if we decide to use them, but what alternatives are there for water and land? As Mark Twain once said, and I suppose it could in some way apply to water as well, "Buy land, there not making it any more".
And this is where it would begin. Deep pocket developers, opportunists hire geologists and hydrologists to find buried reservoirs and secure the land rights, thus obtaining access and distribution rights to the water below. Taking a Daniel Plainviewesque strategy from Tnere Will Be Blood, hostile take overs will ensue, but this time it's not for commodity but a life source with no alternatives. The events proceeding inevitably would lead to violent struggles for any immense water resources.
Assuming we reach a point where water is so scarce it causes military coups and guerrilla warfare, will technology reach a point that will enable us to send our own Ice Pirates out to secure intergalactic resources to replenish our own? As with The Ice Pirates, will we resort to other actions once mocked in Spaceballs, sucking the resources out of the Universe's Druidias?