People have been warned that water supplies from private wells can be contaminted with the dangerous bacteria E.coli.

The HSE has reported a growing number of cases of VTEC, a particularly nasty form of E.Coli that can cause people to get severely ill. Ireland has the highest incidence of VTEC in Europe.

It is estimated that 30% of private wells in Ireland are contaminated by E. coli arising from animal or human waste.

The HSE and the Environmental Protection Agency (EPA) have said analysis of cases finds that people who contract VTEC are up to four times more likely to have consumed untreated water from private wells.

"Lots of people assume that because their water comes from a well or a spring that it's completely pure and safe to drink, but that is not necessarily the case," said David Flynn, Programme Manager, EPA.

"We estimate that up to 50,000 private wells in Ireland are contaminated with human or animal waste and this can cause significant threat to people's health. Sometimes, we find that people can develop immunity themselves, but visitors to the house, particularly children and the elderly are at risk of getting very sick."

According to the HSE, VTEC infection often causes severe bloody diarrhoea and abdominal cramps although sometimes the infection causes non-bloody diarrhoea or no symptoms. Usually there is little or no fever, and patients recover within five to 10 days.

However, in some people, particularly children under five years of age and the elderly, the infection can also cause haemolytic uraemic syndrome (HUS), in which the red blood cells are destroyed and the kidneys fail. HUS is the principal cause of acute kidney failure in children.

Dr Una Fallon, public health specialist in the HSE, said there had been a dramatic increase in the number of cases of VTEC in recent years.

"VTEC is a nasty water-borne illness and cases have been linked to contaminated wells. VTEC infection is most common in children and in up to eight per cent of cases patients go on to develop serious kidney complications. which can on rare occasions, prove fatal. This is all preventable."

The EPA says well owners should check their wells to ensure their health is not at risk. This includes checking that there are no sources of pollution entering their well and testing their water, at least once a year, ideally following heavy rain, when the well is most at risk of contamination.

The agency says disinfection kills all E. coli including VTEC and, while public water supplies are disinfected, not all private wells are.

Find out more about VTEC here