A backflow prevention device is used to protect potable water supplies from contamination or pollution due to backflow. In water supply systems, water is normally maintained at a significant pressure to enable water to flow from the tap, shower, or other fixture. Backflow is the undesirable reversal of the flow of water or mixtures of water and other undesirable substances from any source (such as used water, industrial fluids, gasses, or any substance other than the intended potable water) into the distribution pipes of the potable water system. There are many types of backflow preventers from the simplest to very complicated ones, but their purpose is the same – they are installed to preserve the purity of drinking water in your household.