Name the most common cause for public water supply contamination.

Name the most common cause for public water supply contamination.

• A. Cross-Connection
• B. Contamination by corrosion
• C. Sedimentation
• D. Backflow

Answer: (D)

Backflow is the reverse movement of water into the distribution system, which allows contaminants from consumer plumbing or external sources to be drawn into the public supply. The contaminant actually enters the system when pressure conditions cause water to flow backward, often through a cross-connection that links potable water to a non-potable source. In practice, that backflow event is the direct cause of contamination, whereas the cross-connection is what creates the pathway for backflow to occur.

Other options relate to water quality issues or to setups that could enable backflow, but they aren’t the event that brings contaminants into the system. Corrosion and sedimentation are more about water quality changes within piping or treatment processes, not the contamination mechanism itself.