Escherichia coli
The definitive indicator of recent faecal contamination. E. coli is not usually the pathogen of concern itself; it is present in enormous numbers in faeces, survives in water for a similar time to many pathogens, and is easy to detect — which makes it the sentinel that everything else is judged against.
Key facts
- Contaminant group
- Biological
- World Health Organization — guideline
- Not detectable in any 100 ml sample
- European Union — legal limit
- 0 per 100 ml
- United Kingdom — legal limit
- 0 per 100 ml
- United States — legal limit
- Treatment technique and monitoring requirements
Where it comes from
- Human and animal faeces
- Sewage and septic discharge
- Agricultural runoff
- Ingress into distribution networks through pressure loss or burst mains
How it behaves in water
Does not multiply appreciably in cold water and dies off over days to weeks. Its presence therefore indicates recent contamination, which is exactly what makes it useful as an indicator rather than a nuisance.
How it is measured
Reported as colony-forming units or most probable number per 100 ml. In treated drinking water the standard is absence, so any detection is a failure of the treatment or distribution barrier rather than a matter of degree.
Regulatory position
| Jurisdiction | Value | Status | Notes |
|---|---|---|---|
| World Health Organization | Not detectable in any 100 ml sample | guideline | — |
| European Union | 0 per 100 ml | legal limit | — |
| United Kingdom | 0 per 100 ml | legal limit | — |
| United States | Treatment technique and monitoring requirements | legal limit | — |
Table sources
- World Health Organization — Guidelines for Drinking-water Quality. Public but restricted · CC BY-NC-SA 3.0 IGO
- European Commission — Drinking Water Directive (EU) 2020/2184 and reporting. Open — attribution required · European Commission reuse policy (Decision 2011/833/EU)
- Drinking Water Inspectorate — Drinking water quality in England and Wales. Open — attribution required · Open Government Licence v3.0
- United States Environmental Protection Agency — Safe Drinking Water Information System. Open · US Government work — public domain
Health context
Most strains are harmless commensals. Their significance in water testing is as an indicator that faecal material — and therefore potentially pathogens such as Campylobacter, Salmonella, norovirus and Cryptosporidium — has reached the supply. Certain strains, notably E. coli O157, are themselves seriously pathogenic.
What removes it
| Row | Effective | Not reliably effective |
|---|---|---|
| 1 | Chlorination | Sediment filtration alone |
| 2 | Chloramination | Carbon filtration alone |
| 3 | Ozone | Water softening |
| 4 | Ultraviolet disinfection | — |
| 5 | Membrane filtration | — |
| 6 | Boiling | — |
Relationships
Related intelligence
Sources
- World Health Organization — Guidelines for Drinking-water Quality. Public but restricted · CC BY-NC-SA 3.0 IGO
- Peer-reviewed scientific literature — Open-access hydrology, water chemistry and water use research. Public but restricted · Publisher terms — public access, reuse not clearly granted