You can’t always tell; but in general, once your water breaks, it keeps coming. Ruptured membranes is not just a small gush or a little bit of spotting; if you think your water has broken, clean up and see if the leakage persists. If it does or you are unsure, you probably need to be examined.
Discharge is common in pregnancy but usually never results in more leakage than would fill a small pad or pantiliner. Probably the most common reason why women believe that their water has broken is because they have peed on themselves. Most women cannot believe that they have in fact peed on themselves but in the third trimester, with the baby’s head smashed right against your bladder, this is a common occurrence. If it happens on your bedsheets or in your underwear, you won’t always be able to tell that it is urine by smell or color alone. Amniotic fluid has a unique odor that is like a combination of ejaculate and bleach; that may not be helpful if you’ve never smelled amniotic fluid before, but when you do maybe you’ll recognize it.