I have not had a waterbirth- it doesn't work well for me, but I think anything that doesn't make you shiver should be fine. Keep in mind that cool water combined with air conditioning could make you quite cold. I don't know about you, but when I am cold, my muscles tense and that sort of defeats the purpose of the water in the first place. Since we don't have air conditioning, I like taking lukewarm baths in the summer as a way to cool off-warmer than a pool outside (plus no chlorine!) but definitely cooler than my body. I plan on giving this a try while in labor this time (late June!).