When your eyes become dry and uncomfortable, the tear glands react by producing large amounts of tears, a process known as reflex tearing. Reflex tears contain more water and less mucus and oils than regular tears. Because reflex tears are of poor quality, they don't do a good job alleviating dryness. Even more tears are produced, creating a vicious circle.
Other causes of watery eyes include the following:
- Blocked tear duct
- Allergies
- Eye infections
- Eye irritation
- Blepharitis
- Underlying health conditions
If your eyes are watering, a detailed eye examination by your eye care provider can help identify the cause. Treatment will depend on the cause.
Source:
Fekrat, Sharon, MD and Jennifer S. Weizer, MD. All About Your Eyes. Duke University Press, 2006.

