Condoms: Although they do protect against both pregnancy and STDs, are a risky birth control method to use due to the possibility of them rupturing from decreased lubrication and possible deterioration from heat, chlorine, or oil-based substances in the water (i.e., sun screen, bubble bath, etc). Plus, there is the added threat that the condom could slip off if water gets into it, and a man may not even be aware that this has happened.
Spermicidal methods, such as suppositories, jellies, and foams, are not suitable AT ALL for having sex in the water. If the spermicide is inserted into the vagina, the increased amount of water that enters the vagina during sex will wash it away. Even if some of it remains, the effectiveness of this method will be greatly reduced.
The Today Sponge: Though a woman can be in a bath, Jacuzzi, or pool while the sponge is inserted, it is not recommended that she have sex while in the water since the introduction of the higher quantity of water into the vagina could potentially dilute the spermicide in the sponge.
Diaphragm or Cervical Caps: In addition to not relying on these methods for protection during water sex, a woman should not even take a bath with a diaphragm or cervical cap in place. The water can move the device out of its critical position as well as wash away the spermicide needed for the proper use of these forms of contraception.