We have a swimming pool tutorial coming up and I have been asked repeatedly if mini dolls can get wet in water or not. Yes and no!
If you have an older version with acrylic eyes, don't get the eyes wet.
The water can loosen the glue holding the eye in place.
If you have newer version minis with painted faces GO FOR IT!
Rooted hair and painted faces are no problem - let them swim or take baths. I've even heard some people toss them into the washing machine!