Nasty little buggers! I just found out that my house is infested, I am infested and my indoor, geriatric cats are not, but whatever, they get flea collars for preventative action and I get a flea bath lol. So I came accross this question as I found a live flea, put it in water and it didn't drown as I hoped it would, read this info and put a pump of liquid soap in the glass and stirred, he died before the water settled!
Bathing your cat or dog can drown fleas, and you should keep the animal lathered up in the bathtub or sink for at least five minutes. A bath, however, might not get rid of flea larva or eggs. http://www.alt4animals.com/flea.htm
Fleas will die in soapy water, but can usually jump out of regular water unless you're planning to flush them down a toilet. Most pet owners say that fleas don't even drown in water, so it is better to use flea shampoo if trying to rid your pets of fleas.