Which of the following would be an indicator that a water system might be contaminated?

The presence of coliform bacteria is a significant indicator that a water system might be contaminated. Coliform bacteria are used as a standard measurement in water quality testing because they are typically found in the feces of humans and other warm-blooded animals. Their presence suggests that there is a pathway for pathogens to enter the water supply, indicating potential contamination. The finding of coliforms is a red flag for public health because it signals that drinking water may not be safe and could pose a risk of waterborne diseases.

In contrast, while inconsistent water pressure can suggest system issues like leaks, it does not directly indicate contamination. Color changes in water can be symptomatic of various issues, such as sediment or rust, but do not inherently signify microbial contamination. High chlorine residual levels typically indicate that enough disinfectant is present to kill pathogens; hence, it is generally a positive measure rather than an indicator of contamination.