As for tights in aquatic exercise....I don't think I've ever seen tights worn in a pool.
As for tights in water, I used to do lots of scuba diving, and had a body suit of lycra, much like my unitards for ballet class except with better zippers, for warm water diving. I don;t see why a pair of lycra tights wouldn't work.
Good luck! BalletMaster[/i]