What is the main function of a backflow preventer in plumbing systems?

The main function of a backflow preventer is to prevent contaminated water from entering the potable water supply. This device is crucial in maintaining water quality and public health. Backflow can occur when there is a change in pressure within the plumbing system, which may cause water to flow in the reverse direction and potentially introduce harmful pollutants or contaminants into the drinking water supply. By installing a backflow preventer, plumbing systems ensure that any back pressure or back siphonage is mitigated, protecting the integrity of potable water sources. This is especially important in residential and commercial properties where cross-connections between potable water and non-potable systems could pose serious health risks.

The other choices do not accurately represent the purpose of a backflow preventer; regulating water pressure, increasing water flow, and measuring water usage are functions associated with different plumbing components, but not with backflow prevention.