What is wrong if your eyes water a lot and won't stop?

Epiphora: There are two types of epiphora. One is caused by things that irritate the eyes (like onions or allergies) and cause the lacrimal glands to produce increased tears. The second is caused by blockage of the tear drainage mechanism so that even if the lacrimal glands are producing a normal amount, the tears can't get down the drainage tubes to the nose.