Sushee, my waters broke before I started labour and you really couldn't have mistaken it for anything else. If you were going to pee that much you'd know all about it before it started and it smelt totally differant. When I went to the hospital it ended up all over the floor at reception LOL - no pad on earth could have held it.
I wasn't really put under any pressure when I was in hospital - when I didn't gointo labour they just transferred me to the ante-natal ward and started giving me IV antibiotics about 12 hours later. I went into labour spontaneously the next night (the cow midwife wouldn't believe me and kept trying to moniter me).

I've read once that if you're unsure you can empty your bladder and then tighten your pelvic floor mucles and bear down lightly - if any fluid comes out its likely to be your waters.