Thousands of homes in Surrey and Kent could have tap water contaminated with E-coli after tests discovered the potentially deadly bacteria.
People living in postcodes in Oxted, Redhill, Limpsfield, Godstone and Sevenoaks are being advised to boil their water before drinking it.
The contamination is understood to affect more than 400 postcodes in southern England - the list of areas can be found here.
In a statement, water company SES said: “Our customers in and around Oxted are being advised to boil their tap water after tests showed that water supplies could be affected by the bacteria E-coli.
“The issue was discovered during routine tests, and our teams are working to investigate the problem and restore supplies to their usual high standards.”
It said while they await further test results “which will confirm the scale of any contamination”, customers should boil their water and let it cool, before using it for drinking, preparing food or cleaning their teeth.
Boiled water can be kept in the fridge and should be covered and used within 24 hours. SES said that pets should also be given boiled tap water.
The water company said it was “supporting our most vulnerable customers as a priority” and apologised for the inconvenience caused.
What is E-coli?
E-coli is a bacteria that is found in the gut of most people and animals.
It does not usually cause any problems whilst it is living in the gut, but if the bacteria contaminates areas of vulnerability, such as wounds, catheter sites then infection can occur.