What is a clear sign of excessive swimmer contamination in pool water?

Increased chemical demand is a clear indicator of excessive swimmer contamination in pool water. When swimmers enter the pool, they introduce various contaminants such as sweat, oils, lotions, and other organic materials. These substances interact with the pool's chemical balance, particularly affecting sanitizer levels, pH, and alkalinity.

As more contaminants are present, the pool's sanitation system must work harder to maintain safe and hygienic water conditions. This increased chemical demand can lead to higher usage of chlorine or other sanitizers to ensure that the water remains clean and free from pathogens. When pool operators observe an uptick in chemical requirements, it is a significant signal that swimmer contamination may be a problem, necessitating further attention and possibly additional water treatment measures.

The other options do not directly indicate swimmer contamination. Crystal clear water may suggest good water quality, while consistently warm water is typically related to the heating system rather than swimmer activity. Frequent pool parties might increase the likelihood of swimmer contaminants but do not provide immediate evidence of contamination levels or water quality issues.