Watery eyes can be due to many factors and conditions.

In babies and children, blocked tear ducts are the most common cause of persistent watery eyes. The tear ducts don't make tears. Rather, they carry away tears, like how a storm drain carries away rainwater. Tears usually drain into the nose through tiny openings called puncta in the inner part of the eyelids near the nose. Then the tears travel through a thin tissue layer over the opening that empties into the nose, called the nasolacrimal duct. In babies, the nasolacrimal duct may not be fully open and functioning for the first several months of life.

In older adults, persistent watery eyes may happen as the aging skin of the eyelids sags away from the eyeballs. This lets tears build up and makes it harder for the tears to drain properly into the nose. Adults also can develop blocked tear ducts due to causes such as trauma, infections and swelling called inflammation.

Sometimes, the tear glands make too many tears. This can be in response to the eye surface being dry. Any type of eye surface inflammation also may cause watery eyes, including tiny objects that get stuck in the eye, allergies, or viral infections.

Medicine causes

1. Chemotherapy medicines
2. Eye drops, especially echothiophate iodide, pilocarpine (Isopto Carpine) and epinephrine

Common causes

1. Allergies — Injury, such as from a blunt trauma or burn.
2. Blepharitis — which is eyelid inflammation.
3. Blocked tear duct
4. Common cold
5. Corneal abrasion (scratch): First aid
6. Corneal ulcer.
7. Dry eyes
8. Ectropion — which is an outwardly turned eyelid.
9. Entropion — which is an inwardly turned eyelid.
10. Foreign object in the eye: First aid
11. Hay fever
12. Ingrown eyelash (trichiasis)
13. Keratitis — which is inflammation of the cornea.
14. Pink eye (conjunctivitis)
15. Stye (sty)
16. Tear duct infection
17. Trachoma (a bacterial infection that affects the eyes)

Other causes

1. Bell's palsy (a condition that causes sudden weakness on one side of the face)
2. Blow to the eye or other eye injury
3. Burns
4. Chemical splash in the eye: First aid
5. Chronic sinusitis
6. Granulomatosis with polyangiitis (a condition that causes inflammation of the blood vessels)
7. Inflammatory diseases
8. Radiation therapy
9. Rheumatoid arthritis (a condition that can affect the joints and organs)
10. Sarcoidosis
11. Sjogren's syndrome (a condition that can cause dry eyes and a dry mouth)
12. Stevens-Johnson syndrome (a rare condition that affects the skin and mucous membranes)
13. Surgery of the eye or nose
14. Tumors affecting the tear drainage system