Definition - What does Backflow Preventer mean?
Back flow preventers are special devices used to prevent an undesired reverse flow of water containing contaminants such as bacteria, pollutants or chemicals from entering a clean or potable water supply. Backflow preventer devices are fitted in the water pipeline to stop the reverse flow of water in a pipeline to the potable water source.
Corrosionpedia explains Backflow Preventer
Potable water supplies and many industrial processes require clean and mineral free water. Thus, this water must be protected from any contamination. There is a natural tendency when water is fed from the pipeline at pressure for an undesired reverse flow of water that can pass contaminants from the work site back to the potable water source. This can mismanage the pH levels or lead to an increased chance of corrosion of the structure on which this water is sprayed. Field test equipment is used to test backflow prevention assemblies and so a clear identification of non-potable water can be made at the water storage tank.