What is a backflow prevention device and where do you install it?

A back flow preventer is a check valve that prevents water from flowing backwards into a water supply line resulting in a contaminated water supply. There are degrees of protection ranging from a vacuum breaker on a garden hose line to reduced pressure zone backflow preventers commonly used in a n industrial setting where chemicals are connected to water lines and if pressure was lost on the water supply cross contamination could occur. What is used and where it is installed depends on the application and the treat level. Your local water company should be able to advise what is required and where. ask for their cross connection specialist. a backflow preventor prevents your potable water system from getting contaminated. you can install it where your water main comes into the house. You would also need one if you have a sprinkler system beetween your branch off the main, and where your lines feed into the ground for your sprinklers. This is the best example of what it does. When potable water is pulled through your main line, (when you use your sink, toilet ect.) it can syphone water through one of your branch lines, (sprinkler system line) When the water is syphoned through it pulls whatever is in the line with it. In a sprinkler system whatever you use to improve your lawn can be syphoned through your potable water system through your open sprinkler heads(fertilizers, weed killer ect.). the backflow preventor prevents anything from getting through with a spring loaded valve. Basicaly, like a heart valve it lets the flow of pressure through one way and closes when there is back pressure.