Which indicator organism is used to determine contamination of drinking water?

• A. Iron bacteria
• B. Giardia lamblia
• C. Coliform bacteria
• D. Salmonella

Answer: (C)

Coliform bacteria are used as indicator organisms to assess drinking water quality because they are commonly found in the intestinal tract of warm-blooded animals and their presence signals potential fecal contamination. They’re also straightforward to detect with standard, rapid lab methods, making them practical as a routine measure of sanitary quality. If coliforms are detected, it suggests there could be other harmful pathogens present, prompting additional testing for fecal indicators like E. coli and for specific pathogens.

Iron bacteria, Giardia lamblia, and Salmonella serve different purposes: iron bacteria indicate corrosion-related conditions rather than contamination, Giardia lamblia and Salmonella are pathogens themselves and aren’t reliable as routine indicators of overall water safety.