There's a facet of my magic system that uses a certain kind of crystal to create water out of the magic energy stored within. But, I don't want to solve the entire world's water supply issues with this magic. I'm struggling to think of a restriction that makes it so that infinite water can't be created. I've considered making the water not 100% healthy, but that also kind of defeats the point, especially since that doesn't mesh well with other aspects of the magic system.
So how can I effectively create restrictions to water-based magic so the system cannot create large water quantities?
NOTE: Each crystal corresponds to an "element" roughly, as well as a color. Blue makes water, Red makes fire, etc.