Your waters can break as a huge gush or they can just leak...
If you are waking up in the morning, wet down there and it's not wee, then chances are you are leaking amniotic fluid.
Also if you go to the loo and are able to stop your wee mid stream, your pelvic floor is good. So if you do leak it may not be wee...

Umm, theres another way you can tell but I cant remember...

If you think your membranes may have ruptured definately head to the hospital!