Unlike big cats, domestic cats havelost partial water resistant fur leading water panic since kittenship days for survival purposes.
Instinct
Wet fur makes cats smell different even to themselves, causing great offense to their highly scent-reliant identity.
Scent
Cats hear acutely, so liquid sloshing loudly around their ears feels painfully overwhelming. They retreat to stop the noise.
Sound Sense
Cats run warmer than humans by several degrees. Getting drenched lowers their core body heat rapidly causing great discomfort.
Cold
Water unpredictability and inability to escape sensations quickly crosses instincts making them very leery.
Control
Still water reflecting movements strangely alarms cats when they don't recognize themselves staring back unfamiliar-like.
Looks
Some breeds like Turkish Vans and Bengals don’t mind water. And some individuals break stereotypes and learn to enjoy baths.
Exception