A water main break reduces pressure in a section of the distribution system. Which is a possible consequence?

• A. Increased chlorine residual uniformity
• B. Contamination due to backflow or intrusion
• C. Decreased turbidity
• D. Elimination of pathogens

Answer: (B)

When pressure in the distribution system falls, there is a real risk of backflow or intrusion of contaminants into the pipes. A water main break lowers the pressure downstream, and any cross-connections, leaks, or service connections can pull in water from surrounding contamination sources—soil, groundwater, or sewer-adjacent areas. This intrusion can introduce microbes, chemicals, or other pollutants into the system, even if disinfectants are present elsewhere, so contamination becomes a real concern.

This scenario isn’t about increasing chlorine residual uniformity, and it doesn’t inherently reduce turbidity; in fact, disruptions can cause uneven residuals and may raise turbidity as debris and sediments are stirred up. It also doesn’t eliminate pathogens—the risk of contamination can increase, not decrease, when pressure drops.