Escherichia coli is used as an indicator organism to determine pollution of water with:

Indicators of potential human or faecal contamination or of possible presence of pathogens include Staphylococci, Escherichia coli, faecal coliforms, Enterococci and Pseudomonas aeruginosa. Indicator organisms are used to assess overall sanitation or environmental conditions that may signal or indicate the potential presence of pathogens of food safety concern. It is important to note that indicator species are not necessarily pathogenic.