Chlorinated water can have a deteriorating effect on SKINS fabric, so SKINS advise against wearing your SKINS in the pool. But seawater is fine. Just give your SKINS a good rinse with freshwater afterwards.
SKINS dry out quickly and have a UVP of 50+, so they're great at blocking out the sun. The only thing you might notice is that the gradient compression doesn't work quite as well when you're submerged.