Why use coliforms as indicator organisms in water testing? Choose the best rationale.

Introduction / Context:
Indicator organisms are a practical surrogate for detecting fecal contamination and the possible presence of enteric pathogens. Coliforms, especially Escherichia coli, are widely used in routine monitoring of drinking and recreational waters.

Given Data / Assumptions:

• We are evaluating reasons for using coliforms as indicators.
• Option (a) implies association with fecal pollution and enteric pathogens.
• Option (b) refers to practicality and test specificity.

Concept / Approach:
Coliforms are abundant in feces of warm-blooded animals, often accompanying pathogenic organisms when fecal contamination occurs. Although not perfect (pathogens can occur without coliforms and vice versa), their presence statistically correlates with sanitary risk. Moreover, standardized, specific, and cost-effective assays (e.g., membrane filtration on selective media, defined substrate technology for E. coli) enable routine surveillance.

Step-by-Step Solution:
Link coliform presence to fecal contamination risk and possible pathogens. Acknowledge practicality: rapid, specific tests exist for large sample throughput. Select the option recognizing both relevance and test feasibility.

Verification / Alternative check:
Guidelines for drinking water typically set limits for total and fecal coliforms/E. coli because these assays are reliable early-warning tools.

Why Other Options Are Wrong:

• Only (a): overstates certainty; association is strong but not absolute.
• Only (b): ignores the public-health rationale for using fecal indicators.
• None: incorrect because both reasons contribute to their selection.

Common Pitfalls:
Interpreting coliforms as pathogens; they are indicators, not necessarily disease-causing themselves.

Final Answer:
Both (a) and (b)