What does a backflow preventer do?

A backflow preventer is a crucial plumbing device designed to ensure that water flows in a single direction, preventing contaminants from entering the clean water supply. The primary function of this device is to prevent backflow, which is the undesirable reversal of water flow, potentially allowing dirty water to mix with potable water. By permitting water flow in one direction only, the backflow preventer protects public health and safety.

The other options do not accurately describe the function of a backflow preventer. While increased water pressure can be beneficial in some plumbing applications, it is not related to backflow prevention. Similarly, the ability to reduce the temperature of water, as well as filtering unused water, are functions that fall outside the purpose of backflow prevention devices. Hence, option B effectively encapsulates the primary role of a backflow preventer in maintaining water quality and system integrity.