cats

I dunno how reliable it is, but I've had a lot of cats growing up, and we'd always try to get them used to water when they were still very young kittens, giving them baths in the kitchen sink. Most of my cats ended up tolerating getting a bath into adulthood (I don't think any of them loved it, but they didn't freak out about it), though we had one who was always a crybaby about it, from day one.

Sometimes you just get lucky and end up with a cat that absolutely loves water. I had one that I'd have to lock out of the bathroom whenever I'd shower, because she'd always want to get in the water and start rolling around and try to get under my feet.