Thames Water tested water samples after dozens of residents in south-east London reported sickness and diarrhoea.
The utilities giant confirmed it was testing samples of its water after dozens of residents in Beckenham reported being struck by a stomach bug.
Among those reporting sickness were a four-year-old boy and an adult woman who went to hospital with vomiting and dehydration, reported The Guardian newspaper.
However, Thames Water said there had been “no failures from the Central Sydenham water zone.”
It comes after around 17,000 households and businesses in Brixham, Devon, supplied by South West Water were told not to use their tap water for drinking without boiling and cooling it first.
Katie Cox, a TV producer who lives in the area, told the publication: “I was unwell two weeks ago with what I thought was a stomach bug.
“It was a good week before I was able to eat again properly. Since then, the South West Water contamination has come to light and I became concerned that maybe there is something in our water.”
A Thames Water spokesperson said it collected samples from the area on May 22.
“Initial on site testing carried out by our accredited technician did not indicate an aesthetic issue with the water, further samples were also collected for laboratory analysis and results showed no concerns.
“Customers can find information about their water supply by inputting their postcode on our website.”
The spokesperson added: “We take the quality of our water extremely seriously – it is the highest quality drinking water in the world – and since 2010 more than 99.95% of tests taken from customers’ taps met the standard required by UK and European legislation.
“Every year, we carry out more than 500,000 tests.”
In Brixham, two people were taken to hospital following a cryptosporidium outbreak, a waterborne disease which can cause unpleasant symptoms such as diarrhoea and vomiting.
The number of homes which the “boil water” notice applies to has since reduced by 85%, but SWW said this would remain “until we and our public health partners are completely satisfied it is safe to do so”.
