Sufficiently big AC systems often use water cooling because water is more effective at transferring heat than air, is cheaper than other liquids, and unlike other liquids is not a massive safety hazard if it leaks.

It is why if you want to defrost something quickly, leave it in water rather than in the open air.

Basically, yes. It's about cooling efficiency, cost-effectiveness, practicality and scalability. Water has excellent heat transfer properties, which allows for efficient cooling. As I understand it, solar will have limited capacity and depend on sunlight availability..which obviously fluctuates based on weather conditions, whereas data centers need continuous power supply. Also, cost of installing a large-scale solar power system and maintaining battery storage can be high.

Don’t homes in Arizona mostly use swamp coolers? They’re more efficient as long as you have a water supply

Hell my high school in Illinois had one. If you stood in the wrong spot some days you’d get spritzed because it wasn’t quite evaporating everything.