Which of the following potential contaminants is most likely to affect taste in drinking water?

Hydrogen sulfide is known to significantly impact the taste and odor of drinking water. This compound is often associated with a "rotten egg" smell, which can be quite unpleasant and alters the overall sensory experience of the water. Its presence can make water taste bitter or off-putting, thereby directly influencing consumer perception and acceptance of the water quality.

While iron, calcium, and chlorine can also affect taste, they tend to have different characteristics. Iron can impart a metallic taste, calcium typically does not cause a strong taste but can contribute to scaling and hardness, and chlorine is often used in water disinfection and can give a noticeable odor but is less impactful on taste than hydrogen sulfide. Therefore, hydrogen sulfide stands out as the most likely contaminant to affect the taste of drinking water.