I really don't mean for this to sound heartless, but the thing to do here is to realize that you live in a desert and start using water accordingly. Don't grow lettuce! Charge more for greens fees at golf courses! Use better irrigation methods! It would make sense for the Spanish government to cushion the transition to a less water-intensive lifestyle in the region, but the reality is there's plenty of water almost anywhere for routine human consumption if you use it carefully. This can come about either as a result of water markets or through more heavy-handed regulation (preferably the former), but the first step is for government to stop making the problem worse by stoking unrealistic expectations about abundance.
Obviously, in the real world politics make the resolution more difficult because people are irrational and politicians have short-term incentives to pander. And it's true that if entire countries dry out, that would necessitate wrenching changes on a society-wide scale, since cross-border mobility is low. But we're not close to that point yet.