Swimming costumes are often sexy as hell, and days by the pool bathing in the sunshine and enjoying a few fruity cocktails can be an erotic experience for many. If you can get around some of the more obvious problems (lack of lubrication, nothing to brace yourself against, a potential for being caught) swimming pool sex is a fantastic way to bond with a partner and try out something new. If you get the chance to explore, do try it out - there's a lot to be said for getting down and dirty in the cool water on a hot summer day!
So there are two main issues with sex in the water. One is that it tends to wash away a lot of the essential lubrication, meaning that things can get a little paradoxically dry down there - and the other is that water's natural buoyancy means it can be a bit more difficult than you might imagine getting everything in place. The trick is to bring some water-based lube in with you, anchor yourself on the side of the pool and keep experimenting till you find something that works for you and your partner! This is an experience well worth having, though it might take a little while to get it right.