why do my eyes get watery when i have a cold??

Answer 1

The eyes are kept moist by tears that are constantly washing the eyeball. Normally, you don't notice it because the tears run across the eyeball into the nasolacrimal duct (small tube at the inside corner of your eye) and into your nose where they drain into your throat. When you have a cold, the tissue around the ducts swells, causing the ducts to close, causing overflow of tearing. Hence, watery eyes.

Answer 2

Allergic reaction. You're nose is stuffed, and, since the nerve sensors for the two are so close, they are intertwined. It is similar to when somebody gets severe ear pain from having an abscessed lower tooth.