Add to this the changing external conditions — hot, cold, dry or dusty environments and it’s surprising the whole system copes so well. When the tear film quality is reduced, our eyes may feel dry and gritty. Sometimes if they become irritated enough, the eye responds by flooding the eyes with tears. Thus 'watery' eyes can be a symptom of an underlying 'dry' eye problem!
Persistent watery eyes can indicate a problem with the drainage of tears from the eye. Ideally, the eyelids sit in close to the eyes, and remove a little bit of tear fluid each blink. But if the eyelids are a bit floppy, or if the drainage pathway is blocked, tears will find another way to leave the eye, usually 'leaking' out the corner.