When your waters break it can be anything from a very large gush to just a small wet patch on your undies. To get an idea if it is your waters or not try this:-
Go to the toilet and have a wee, make sure that you empty your bladder. Now stand up and have a couple of big coughs. Stand in front of the sink with your feet apart. Put your hands on the sink and lean forward as if you were vomiting. (ah remember that position from the first trimester!!!!). Now sway your hips in a circular motion. If you get a leak when you cough or when you swing your hips then there is a chance that your waters have broken.
Just remember that these tests are not perfect and are only a guideline. If you are unsure it would be a good idea to get things checked.