Runny eyes in dogs can be due to some problems that can develop due to irritation in the eyes or abnormal tear drainage. Irritation in the eyes can be due to conjunctivitis caused by bacterial/viral infection, glaucoma, and problems in the eyelids .Sometimes, skin hairs can reach to eyes or abnormal growth of eyelashes can cause irritation. Allergy to smoke, dust and air pollution etc can cause watery eyes. So, it will be ideal to take your dog to vet.