What is the purpose of a backflow preventer in a hydrant supply line?

• A. To increase water pressure in the hydrant line.
• B. To filter water before it leaves the system.
• C. To prevent contaminated water from flowing back into the public water supply.
• D. To regulate the flow from the hydrant.

Answer: (C)

The purpose of a backflow preventer in a hydrant supply line is to stop water from flowing backward into the public water system, protecting that supply from contamination. When pressure in the hydrant line drops or a connection creates a downward flow (back-siphonage), a backflow preventer acts as a one-way barrier so water can only move away from the street main and not back into the municipal system. This is crucial during firefighting operations where hoses or connections could introduce used, dirty, or otherwise unsafe water into the supply if backflow were possible.

Other functions like increasing pressure, filtering water, or regulating flow aren’t the goals of a backflow preventer. It isn’t designed to boost pressure or remove contaminants, and it doesn’t control the rate of flow. Its sole job is to maintain a safe, unidirectional flow to prevent contaminant entry into the public water supply.