What does the presence of E. coli in water indicate?

The presence of E. coli in water serves as a strong indicator that the water has been contaminated with sewage or fecal material. E. coli is a type of bacteria that normally resides in the intestines of warm-blooded organisms. Thus, when it is detected in water sources, it typically suggests that there has been a recent introduction of fecal waste, which could pose serious health risks. This contamination can lead to the spread of waterborne diseases because E. coli strains, particularly those that are pathogenic, can cause gastrointestinal illness and other health issues if ingested.

In contrast, assertions about water being clean and safe to drink without contaminants would be unfounded in the presence of E. coli, as its existence directly contradicts that notion. Additionally, contamination from chemical pollutants does not correlate specifically with E. coli presence, as this type of contamination involves different indicators. Likewise, while high levels of nitrates can exist in water contaminated by agricultural practices or sewage, nitrates themselves are not directly connected to fecal contamination like E. coli is. Therefore, the identification of E. coli signifies a clear public health concern related to sewage contamination, marking it as the correct answer.