What is the recommended combined chlorine level in a pool for optimal sanitation?

The recommended combined chlorine level in a pool for optimal sanitation is indeed in the range of 0-0.2 ppm. This level is significant because combined chlorine, which results from the reaction of free chlorine with contaminants in the water (such as sweat, urine, and other organic matter), can lead to issues like unpleasant odors and eye irritation, which may affect the swimmer's experience.

Maintaining combined chlorine well below 0.2 ppm is ideal, as it indicates that the majority of the chlorine in the pool is free chlorine, which is effective in disinfecting and sanitizing the water. Higher levels may suggest that sanitation is suboptimal, leading to potential health concerns and a need for additional shock treatments to break down the combined chlorine compounds.

In comparison, higher levels identified in other choices may not indicate optimal sanitation. For instance, levels above 0.2 ppm can imply that the pool's chlorine is being utilized up by contaminants rather than remaining free and available for disinfection purposes. Keeping combined chlorine levels low helps ensure a safer and more pleasant swimming environment for users.