What is a common indicator of unsanitary drinking water?

The presence of coliform organisms is a common indicator of unsanitary drinking water because these bacteria are found in the environment, particularly in the feces of warm-blooded animals. Their presence suggests that the water may be contaminated with pathogens that can cause serious health issues, such as gastrointestinal illness. The detection of coliforms, especially E. coli, in drinking water signals that there could be a breach in the water's treatment system or contamination from sewage or animal waste, making it unsafe for consumption.

While dissolved solids, high pH levels, and excess mineral content can affect water quality, they do not directly indicate microbial contamination. Therefore, testing for coliform organisms is critical for assessing the microbiological safety of drinking water.