how do faulty sewer lines increase the risk of water borne disease?

Faulty sewer lines can cause deadly effects upon human being by increasing the risk of water borne disease. One of the most common ways this happens is by mixing of drinking and waste water which increases the risk of contracting cholera. Other water borne disease may be caused by exposure of water from sewer to the surface by either blockage or broken sewer line, which increases problems with water borne viral and protozoan disease.