His eyes my actually be dry and irritated causing the watering. See an ophthalmologist.

Some watering is expected soon after surgery. It should subside after a few days. Go back to his surgeon for review.

Eyes usually temporarily get dryer after cataract surgery. In the immediate post-op days, he could be feeling the incision, which can make him tear. When the eye gets dry, we get reflex treating. Try non-preserved artificial tears. If this is not enough, there are other drops and procedures that could help, but you would need to see an eye care professional.

This question is best answered by the doctor who did his surgery and has examined him. If this doesn’t adequately address the problem he should get another opinion.