E. coli in UK Drinking Water

Health Effects

While most E. coli strains are harmless, some produce toxins that can cause severe illness. E. coli O157:H7, the most dangerous strain, can cause bloody diarrhoea, kidney failure (haemolytic uraemic syndrome), and in rare cases death — particularly in children and elderly people. Any detection in treated water is treated as a serious public health event.

Where It Comes From

E. coli reaches water sources through sewage discharges, agricultural runoff carrying animal waste, and combined sewer overflows during heavy rainfall. In treated water, detection usually indicates a failure in the treatment or distribution system — such as a broken pipe, cross-contamination, or a treatment plant malfunction.

Regulatory Standards

How to Remove E. coli

• UV disinfection

  Ultraviolet light at 254nm wavelength damages the DNA of bacteria and viruses, preventing them from reproducing. Highly effective against microorganisms without adding chemicals to the water.

• Reverse osmosis

  A membrane filtration process that removes up to 99% of contaminants by forcing water through a semi-permeable membrane under pressure. Highly effective but produces some wastewater.

• Chlorination

  Adding chlorine or chloramine to water kills bacteria and viruses. The standard disinfection method used by UK water companies. Effective against E. coli and most waterborne pathogens.