There is a wide variety of waterproof vibrators available for playing
in the tub. There are waterproof versions of rabbit vibrators,
bullets, contour vibes, phallic vibes, pocket rockets; just about any
battery-operated vibrator you can think of, there's a waterproof one.
However, you have to look for a vibrator that specifically says it's
waterproof. If it's not, getting it wet will probably ruin it.
Never, ever use an electrical (plug-in) vibrator in the bath or hot
tub. You will probably electrocute yourself.