How safe is YOUR tap water? We reveal all the scary pathogens that could be lurking in your supply

Hundreds of people in Devon have been urged to “not drink” tap water without boiling it after a microscopic parasite infiltrated their water supply.

South West Water revealed “small traces” of cryptosporidium, commonly known as “crypto”, They were found in the water at Brixham.

The chlorine-resistant parasite, which can cause vomiting, stomach pains and fever, can survive in water for up to a week.

It is transmitted through contaminated fecal matter that enters the mouth.

So how safe is tap water? And what else could be lurking in your offering? Could it be doing any harm?

Our interactive graphic below shows the key pathogens we might unknowingly drink every day.

The specific level of substances detected varied across the country and represents only tiny traces per liter. Of the thousands of tests performed, only a small fraction returned a positive result above threshold levels.

Figures from the Government’s Drinking Water Inspectorate (DWI) suggest that bacteria normally found in our intestines can sometimes be found in tap water.

Both types measured by regulators (E. coli and enterococci) can, in theory, make people sick, although for most people this is usually mild.

Instead, their presence is typically measured as an indicator that water supplies may have been contaminated by human fecal matter.

Therefore, the DWI sets the limit at 0 bacteria per 100 ml, which means that, at least in principle, this type of bacteria should never be detected in household supplies.

However, this is not the case as 27 breaches were detected in 2022. The vast majority (12) were from Severn Trent Water, which supplies 4.5 million homes and businesses in the Midlands.

And at least 5,577 Britons on private supplies drank water contaminated with faecal matter in 2022.

Professor Paul Hunter, a renowned infectious diseases expert at the University of East Anglia who has advised the WHO on standards for drinking water, said these pathogens are unlikely to make a Briton sick, but are good indicators of pollution.

“They are generally not dangerous in and of themselves, but they are an indication that the water may have been contaminated by fecal matter,” he said.

‘There are some types of E. coli that can cause potentially severe diarrhea, but the most common type would often not test positive even if it were present.

“Therefore, the presence of an E. coli or Enterococcus indicator does not mean that disease-causing bacteria are present, we just cannot say that they are absent.

“You could probably drink water with enough indicator bacteria without getting sick. But the indicators are present and it cannot be ruled out.’

Another thing that can cloud the data, he added, is that people often contaminate their own tap water by accidentally touching the tap opening while washing their hands after using the bathroom.

This places the bacteria right at the tap opening and is therefore not an indicator that the supply itself is contaminated.

Professor Hunter added that British drinking water is generally very safe and the fact that only 27 tests came back positive, out of more than 150,000 carried out, was in fact a “good” result.

However, yesterday, UK Health Security Agency (UKHSA) officials said 22 cases of cryptosporidium infection had been confirmed in Brixham.

For most people, cryptosporidiosis (the technical name for the infection) is mild.

It usually goes away on its own without any treatment within a few days or weeks.

However, for vulnerable people, such as those with weakened immune systems and the elderly or patients undergoing cancer treatment, it can be more serious.

Due to its highly infectious nature, people with symptoms such as diarrhea and vomiting are told not to go to work or school until they have been free of these symptoms for at least 48 hours.

DWI figures also suggest that pesticides – chemicals manufactured to kill unwanted weeds and bugs – can enter British water supplies through run-off from gardens and farms, as well as other sources.

The DWI sets a limit of 0.5 μg/L for the total amount of all pesticides in tap water, but is set at 0.1 μg/L for some specific types.

The latter limit was exceeded three times in 2022, all by water supplied by Northumbrian, Essex and Suffolk Water Ltd.

Other chemicals include PFAS, called “forever chemicals” for their ability to persist in the environment for years, copper, iron and even nickel.