My baby is 9 months old and since birth her left eye waters all day. will it resolve on its own? is this something i should be worried about?

Lacrimal blockage: Your baby has a blockage at the lower end of the lacrimal "plumbing" that goes from the eye into the nose. As many as 2% of babies have this but many of those spontaneously open by age 6 months. After that the percentage drops. You should see a pediatric ophthalmologist to evaluate this and consider a short procedure called a probing which will open things up.