I use a Venus razor, with disposable heads. I use the same one for weeks on end, to do pits daily and legs every other day. It comes with a hard plastic case for the cartridges, on top of which the razor sits, never going rusty. I buy the packs of heads on Ebay, much cheaper than the supermarkets.
I have tried electric shavers, but it takes longer to do and doesn't get so close. I also tried an epilator but couldn't stand the pain!
I hope you enjoy the swimming, take it gently!