Cats are really superstitious creatures. I have done a lot of research on this, and have narrowed it down to three possibilities. First, cats are not fond of religion and are scared that they may end up being accidentally baptized. Trust me, they'll not be the same after if you baptize your cat. Second, they actually love water, but they never want you to know what truly excites them. It will give you too much power. When it looks like they're resisting the water, inside they're actually overwhelmed with happiness. Third, they are extremely afraid of both the loch ness monster and sharks. (The movie jaws changed cats everywhere, and not for the good) any time they are in water, they are afraid that they will be swept out to sea and be killed by one of those two monsters.
I'm still working on my research and I will keep you updated when I have a conclusive answer.
Cats hate water because their fur becomes waterlogged. This usually weighs them down and they become uncomfortable. Cats are naturally skittish although not all cats hate water. For instance, wild cats can swim across streams.
I've had some that love being in the tub/shower with me. Then again, I have 4 dogs right now that scream abuse every time I put them near a faucet (for a bath)...I'm not certain hatred for water matters the species. In fact, I have a very low tolerance myself, but do enjoy being clean!