People develop watery eyes for one of two reasons, and sometimes a combination of the two.

Firstly, and most commonly, the eyes may water if there is some irritation present around the eye, for example irritation of the eyelids (blepharitis), allergy or a lump on the eyelids.
Another reason for the eyes to water is if there is any nasal irritation.
In these cases eliminating or reducing the cause of the irritation should help with the symptoms.

Secondly the eyes water if there is a blockage of the drainage system (nasolacrimal duct) around the eye, preventing the normal tears from draining away so that they overflow and run down the cheek. The most common cause of this is a narrowing of the nasolacrimal system with age called nasolacrimal duct narrowing or obstruction. It can also sometimes occur after trauma or an eye infection.

Normal anatomy of the nasolacrimal system

PICTURE

If there is a narrowing or blockage of the nasolacrimal duct, then surgery is usually required to create an alternative passage for the tears to drain away. The operation is called a Dacrocystorhinostomy (DCR for short).