An example would be a boiler operating at 100-150 lbs. Since the district's water pressure is usually about 60 lbs. and water flows in the direction of least resistance, back pressure would be created. The contaminated water could flow into the drinking water supply. What is backflow prevention assembly. A backflow prevention assembly is a testable, mechanical device that uses check valves to prevent polluted or contaminated water from flowing backwards.
Some assemblies eliminate backflow by discharging used water to the ground.
Assemblies installed as a secondary protection should be located as close as possible to the water meter. A check valve is not equipped with test connections to assure that the valve is preventing backflow. That's why only approved assemblies are allowed. An approved assembly is any type of backflow prevention assembly that has been tested and approved by an independent testing laboratory and the Water District. State regulations currently exempt single-family homes used solely for residential purposes from assembly requirements.