Who ever heard of a HRM that's allergic to sweat! LOL!
No matter what you get, you will want one with a chest strap. The wristwatch ones generally require you to stop what you're doing to check your heart rate, which a) slows it down (since you're stopping), b) is inconvenient, and c) is inaccurate since it tries to fill in the blanks when you're not checking your heart rate. Also, HRMs are really only accurate for cardio - heart rate increases are the effect of rhythmic movement, rather than the cause. It's just the one thing that's measureable.
As far as recommendations, I really like my Polar. I'm not sure if the one I have is waterproof because I don't have access to a pool anyway so that function wasn't important to me, but if you go to their website you can sort devices by what features you want, waterproof being one of them.