Why do cats hate water so much?  Lots of animals don't enjoy getting
rained on or falling into a pond, but with cats it goes far beyond
that, to the point of an irrational phobia.

All the cats I've owned completely freak if even a single drop of
water falls on them, causing them to take off running then
proceeding to groom themselves to get rid of the wet spot.  It
is like they are traumatized by even the slightest amount of
water.

My last cat HATED the swimming pool.  I would carry her out back
and as I approached the pool she would claw her way out of my
arms and escape.  My current kitty is the same way.  She likes
to look into the toilet, but freaks out in terror if I flush it.
The same for the washing machine.

One of the great joys of life is giving a cat a bath (sarcasm).
I haven't bathed my new kitty yet, but I gave a bath once or
twice a year to my last cat.  I would take her into the shower
and close the sliding glass door then turn on the water.  She
screamed so loudly, it sounded like I was torturing her with
a blowtorch!  I mean, it was just warm water and she reacted
like it was sulfuric acid or something.  After the bath was
over I would dry her off then she would proceed to lick herself
compulsively, as if that would make her cleaner than she
already was.