Backflow prevention is the method used to prevent polluted water from poisoning the water supply. Backflow devices or preventers are used to stop chemicals, oils, pesticides, fertilizers and so on from making their way to your kitchen faucet or bathtub. Backflow valves are required on any water system that has the potential to cause contamination. Building architects will design a plumbing system with backflow preventers and the county will demand one in many circumstances for public safety. Testing is necessary for all backflow valves to certify that they function as designed. Only trained technicians with a state certificate are allowed to test and submit backflow forms back to the water agency or county.