If three consecutive water samples from one supply all show the presence of E.coli, what does this indicate?

The presence of E. coli in three consecutive water samples indicates a significant risk of contamination, particularly from human fecal matter. E. coli is a type of bacteria commonly found in the intestines of humans and warm-blooded animals, and its detection in drinking water supplies strongly suggests that there has been a breach in the water source's integrity, granting access to pathogens typically associated with fecal pollution. This can occur due to various factors, such as failures in wastewater treatment systems, agricultural runoff, or contamination from septic systems.

Reliable water quality monitoring typically flags repeated instances of E. coli as a critical public health concern. The continuity of detecting E. coli across three samples strengthens the evidence of ongoing contamination rather than a sporadic or isolated incident. It necessitates swift evaluation and remedial actions to safeguard public health—such as identifying the source of contamination and implementing water treatment or source protection measures.