Backflow prevention devices are installed in the water systems to prevent contamination of pure water, in case polluted water flows backward. They come in various ranges and sizes. One of these is the vacuum breaker. It is mostly used in urinals and toilets. It comes in 2 types: these are the atmospheric and the pressure vacuum breaker. The difference between the 2 is in their structure and cost. Other types of backflow prevention devices include, but not limited to the air gap, the chemigation valve, the double check valve and the anti-siphon valve.