Well, generally speaking, it is kind of normal for many people to have watery eyes, when they go to bathroom. And of course, there are some reasons. According to some researches, someone may have watery eyes when he or she goes to the bathroom if he is having a bowel movement and straining himself. And we can say that the hot momentum in the bathroom can just irritate your eyes, leading to some high eye pressure in your eyes. In that way, it will just affect your tear system. Finally, your eyes will keep watering. Otherwise, there is no reason to have watery eyes in the bathroom. Maybe that is the answer.
This is maybe there are some kind of allergen in your bathroom that can easily cause your eyes watering. It is possibly a bar of soap with a kind of flower fragrance which your eyes feel allergic with. Or it may be a air freshener in the bathroom that irritates your eyes. You can trying removing these things and see whether your eyes is still watery or not. If you still get watery eyes in the bathroom, you should go to the doctor's for an eye examination to see what exactly the problem is.