What presence in water is a strong indicator of fecal contamination?

The presence of coliforms in water is a strong indicator of fecal contamination because these bacteria are commonly found in the intestines of warm-blooded animals, including humans. When coliforms are detected in water, it suggests that the water may have been contaminated with fecal matter, which can introduce pathogenic microorganisms that pose health risks to humans.

Coliforms, particularly fecal coliforms like Escherichia coli (E. coli), are used as an indicator organism in water quality testing because they are relatively easy to measure and their presence correlates with the potential presence of harmful pathogens. Water systems are often monitored for coliform bacteria to assess their safety and potability, making it a critical component of water quality management.

Other options, such as chlorine, are used as disinfectants in water treatment and do not indicate contamination. Pseudomonas can be found in a variety of environments, not specifically linked to fecal matter, while nitrates may indicate agricultural runoff or sewage but are not a direct indicator of fecal contamination like coliforms are. Therefore, coliforms serve as the standard marker for assessing water contamination related to fecal sources.