Backflow is a term in plumbing for an unwanted flow of water in the reverse direction. Backflow is caused by cross-connections that have the potential of allowing contaminants into the drinking water system. City Certified Backflow Prevention offers testing, repairs, and installations. Servicing Oakdale CA., Modesto CA., Turlock CA., Ceres CA., Atwater CA., Stockton CA., Manteca CA., and Newman CA. water companies