Which substance may be added to municipal drinking water to improve clarity?

The correct choice involves the use of aluminum in the form of aluminum sulfate, commonly known as alum, which is frequently utilized in water treatment processes to enhance water clarity. This occurs through a process called coagulation. When alum is added to water, it reacts to form small particles that bind together, aggregating impurities and suspended solids. As a result, these larger clumps of material can be more easily removed through sedimentation or filtration, leading to clearer drinking water.

The other options do not serve the same purpose in water treatment. Bleach, while it can disinfect, is not used to improve clarity but rather to eliminate pathogens. Potassium does not play a significant role in clarifying water; instead, it is often monitored for its levels in drinking water due to health considerations. Zinc, although it can be beneficial in small amounts, is typically not associated with water clarity and, in higher concentrations, can actually be harmful to aquatic life and complicate drinking water quality. Therefore, aluminum stands out as the appropriate choice for improving the clarity of municipal drinking water.