Which situation is most likely to lead to contamination of a water supply?

The situation that is most likely to lead to contamination of a water supply is the presence of a cesspool next to that water supply. This is because cesspools are designed to collect and retain waste, including sewage and other contaminants, which can easily leach into the surrounding soil and groundwater if not properly managed. The proximity of the cesspool to the water supply increases the risk of harmful pathogens, nutrients, and chemicals entering the water source, potentially making it unsafe for human consumption and use.

In contrast, while runoff from a chicken farm can contribute to water contamination due to nutrients and pathogens from animal waste, the direct and immediate risk presented by a cesspool's close location to a water source makes it a more critical concern. Contaminated rainwater can also introduce pollutants, but its impact may be less direct and mitigated across a larger area. Industrial waste drainage is a serious issue as well; however, it typically involves regulated discharges that may not occur at the proximity level of a cesspool. Therefore, the cesspool presents a more straightforward and direct threat to water supply contamination.