A main break may cause low pressure in the distribution system, which in turn may result in...

Low pressure in a water distribution system can create conditions conducive to backsiphonage, which is a flow reversal that can draw contaminants into the system. When the pressure in the pipes decreases significantly, it may allow external fluids, potentially contaminated, to enter through cross-connections or breaches. This poses a significant risk to public health, as it can lead to the introduction of harmful substances into the clean water supply.

Other options do not directly relate to the consequences of low pressure. Ice formation in the pipes typically occurs in freezing conditions, often unrelated to pressure changes. The increase in chlorine residual is generally associated with factors like water treatment processes, not directly with pressure issues. Water hammer, which is a pressure surge caused by rapid changes in flow, usually occurs due to abrupt valve closures or pump failures, rather than low pressure scenarios.