Cats don’t really hate water.
Cats actually are known fishers, and in the wild can sometimes be found cooling in pools of water.
What cats are is incessantly neat.
When water gets on a normal house cat, the cat responds to the droplets just as it would food or dirt particles, as something that needs to be cleaned off with a good tongue bath.
This can be tiring, so cats tend to shy away from situations that might make them have to bathe themselves, including, ironically, baths.