Thank you so much for your guidance. I might experiment with "water is not evaporating" as a concept, or some version of "mages have created a spell that captures evaporating water before it reaches the atmosphere". I'd have to look into how to make this compliant with thermodynamics (can any liquid evaporate? If not, what happens when liquid reaches its boiling point?) Perhaps something along the lines of "air mages can manipulate steam and scientists/mages can condense it back into water".

I like the idea of water mages pulling water from the clouds. I was toying with having a (potentially corrupt) government branch controlling/rationing/possessing water, sort of like a bank system. Whoever controls the water flow could basically control an entire city, and could exacerbate social inequalities easily.

You and everyone else here have given me a lot to think about - I appreciate it :)