Which test is commonly used as an indicator of possible drinking water contamination?

• A. Turbidity
• B. Chloride
• C. Coliform bacteria
• D. pH

Answer: (C)

Coliform bacteria testing is used because it acts as flag that drinking water may have been exposed to contamination. Coliforms are a broad group of bacteria commonly found in soil, vegetation, and the intestines of animals and humans. Their presence in a water sample suggests that a pathway for contamination exists—such as a breakdown in treatment barriers, a leak, or a cross-connection—so there’s a potential for harmful pathogens to be present even if they aren’t detected directly.

Because of this, utilities rely on routine coliform screening as an initial safety check. If coliforms show up, further testing for specific pathogens (like E. coli) is typically performed, and actions such as additional disinfection, flushing, or public notices may be required.

Turbidity, while useful for indicating particulate matter and some treatment process issues, is not a direct indicator of contamination by microorganisms. Chloride and pH are important water quality parameters for corrosion control and overall water chemistry, but they do not reliably signal the presence of contamination in the same way that coliform testing does.