It’s possible 400 postcodes could be affected by the potential contamination of water in Surrey with E. coli.
The issue was discovered during routine tests, according to SES Water, with teams now working to investigate the problem and restore supplies to their usual high standards.
Homes in Godstone, Westerham, Redhill, Lingfield and Horley are all thought to be affected.
Customers in and around Oxted are being advised to boil their tap water following the initial tests by SES Water.
Escherichia coli (E. coli) bacteria normally live in the intestines of healthy people and animals and most types are harmless or cause mild diarrhoea.
However, some strains can cause severe stomach cramps, bloody diarrhoea and vomiting.
SurreyLive will be providing live updates on the investigation by SES Water and the situation across the county in the blog below.
Sign up to our daily newsletter to get more news from SurreyLive straight to your inbox. Find out how here.