Fecal indicator organisms (FIO), also known as fecal indicator organisms (FIB) — primarily E. coli, Enterococci or coliforms — are bacteria that originate in the intestines of warm-blooded animals. Their presence in water signals fecal contamination and the potential presence of pathogens such as Salmonella, Norovirus, or Cryptosporidium. Monitoring FIO (FIB) is the standard approach to assessing microbiological water safety under WHO guidelines and the EU Drinking Water Directive.