My daughter is 5month old aand her right eye is constantly watering what can it be ?

Tear duct blockage: This is common.Given some time & growth the blockage can clear on its own as the tear duct becomes larger.If still blocked at 6m & unresponsive to simple measures, an ophthalmologist may need to probe the duct & clear the blockage.One simple measure involves rolling the tip of the finger over the inner corner of the eye from nose toward eye.That flushes the tear sac & can flush out debris