I'm too prone to infections and there are nasty things in tap water that don't belong inside of the vagina. Hot tubs, especially public hot tubs, are breeding grounds for organisms...it just squicks me out.
I wouldn't in public pools or hot tubs, but pools (and pool tables!), showers, and bathtubs can be a lot of fun. I have some mobility issues, so the slip factor is one that prevents me from much action around water!