The presence of total coliforms in drinking water most strongly indicates which of the following?

• A. The presence of pathogens
• B. The absence of adequate chlorine residuals
• C. The existence of an urgent public health problem
• D. The potential presence of pathogens

Answer: (D)

Total coliforms are indicator bacteria used to assess drinking water quality. Their presence signals that the water may have been exposed to contamination, including sources that could harbor pathogens. While coliforms themselves aren’t necessarily harmful, their detection means there’s a real possibility that pathogens are present, so further testing (for fecal contamination like E. coli) and corrective actions are warranted. This is why the most accurate interpretation is that there is the potential presence of pathogens. The other options don’t fit as well: coliforms don’t by themselves prove pathogens are present, nor do they directly determine chlorine adequacy or automatically denote an urgent public health problem without additional context.