Irrigation system backflow prevention devices are used to protect water supplies from contamination or pollution. Irrigation backflow devices are designed for installation on potable water lines to protect against both back-siphonage and back-pressure of contaminated water into the potable water supply. Many people ask what is a back flow preventer?, do I need one?, and why is it necessary The importance of one is because the landscape around home or business is filled with all sorts of things, that can make people sick if indigested. from fertilizers and bacteria found in pet waste for example. Most irrigation systems are attached to a potable water system. So in other wards the back flow preventer prevents the back flow of contaminated water getting into the potable water supply. Back flow can occur when there is a sudden water pressure drop in the water line. A back flow preventer is something that you might want to question having when installing or repairing a irrigation line.