One of the reason that causes your only one eye watering may be that this eye get irritated by some foreign objects inside the eye socket, such as a sand, dust, eyylash, and so on. You can use clean flowing water to wash the foreign objects out of your eyes. Or you can use clean towel or facial tissue to slightly wipe that out of your eyes, and then apply some antibiotic eye drops into your eyes, and take a rest after that. But if the condition is serious, it may be that one of the lacrimal passages is blocked off, thus making the normally secreted tears flush out of the eye socket instead of getting discharged into the nasal cavity. In this case, you can take a lacrimal passage irrigation in the hospital. You need to go to the doctor's to have an examination first.