What causes backflow into a public water system?

Backflow into a public water system primarily occurs when there is a connection between potable water and another source that has a lower pressure. This creates a situation where the water pressure drops below atmospheric pressure, allowing water to flow backward into the potable supply. The potential for backflow is especially dangerous because it can introduce contaminants from non-potable sources, leading to health risks for users of the water system.

Understanding pressure dynamics is essential here; if the pressure of the potable water drops—either due to high demand, a break in the pipe, or other factors—it can create a vacuum that pulls water from the linked lower-pressure source back into the clean water supply. This is why maintaining proper pressure and ensuring there are no connections to unapproved or unsafe water sources is critical in water system management.

The other options highlight various factors related to water quality or pressure dynamics but do not directly address the mechanics of backflow. For instance, an unrestricted water source refers to the availability of water but doesn't inherently imply a risk of backflow without the pressure factors at play. Improper filtration and elevated levels of dissolved minerals can affect water safety and quality, yet they do not influence the backflow mechanism directly.