Protecting private wells from microbiological contamination
19 June 2014
The Environmental Protection Agency (EPA) and the Health Service Executive (HSE) are advising people that water supplies from private wells can be contaminated with E. coli. It is estimated that 30% of private wells in Ireland are contaminated by Escherichia coli (E. coli) arising from animal or human waste. According to the Central Statistics Office, there are around 170,000 private wells in Ireland.
The HSE meanwhile reports a growing number of cases of verotoxigenic Escherichia coli (VTEC), a particularly serious and nasty form of E. coli. Analysis of cases shows that people treated for VTEC are four times more likely to have consumed untreated water from a private well. The EPA has developed a new assessment tool called ‘Protect Your Well’. Well owners are urged to use it to assess their private well and ensure they are not putting their health, or the health of family and visitors, at risk.
“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.”
VTEC are a particular group of the bacterium E. coli. 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-ten days. VTEC infection is most common in children (60%).
In some persons, particularly children under five years of age and the elderly, the infection can also cause a complication called haemolytic uraemic syndrome (HUS), in which the red blood cells are destroyed and the kidneys fail. This happens in up to 8% of cases. Some people are left with lifelong kidney problems, which can, on rare occasions, prove fatal.
Dr Una Fallon, public health specialist in the HSE and chair of the HSE National Drinking Water Group, said there has 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,” she said. “VTEC infection is most common in children and in up to 8% of cases patients go on to develop serious kidney complications. These can, on rare occasions, prove fatal. This is all preventable.”
IRELAND’S HIGH VTEC LEVELS
Ireland has the highest incidence of VTEC in Europe. Since 2011, the HSE has reported a doubling of the number of VTEC cases in Ireland (284 in 2011, 554 in 2012 and 704 in 2013). Animals, particularly cattle, are the main source of VTEC and infection is spread either from direct animal contact or through contaminated food and water. Person-to-person spread is also common. In other countries, the most common source of infection is through food outbreaks.
In Ireland, rural families are commonly affected and much of this is because of contaminated private wells. Consumers of water from private wells at much greater risk of VTEC than those who drink water from mains supplies. It can take a long time for the bug to clear, even after the child has become well.
Disinfection kills all E. coli, including VTEC and, while public water supplies are disinfected, not all private wells are. “Well owners should check their wells to ensure their health isn’t at risk,” said David Flynn. “This includes checking that there aren’t any 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.”
Poorly constructed wells run the risk of surface water ingress, either directly over the top of the borehole casing and into the groundwater (if the wellhead is below ground or flush with the ground or in an area liable to flooding) or down the side of the casing (if it has not been properly grouted and sealed after drilling). In such cases, surface water contaminants such as VTEC and Cryptosporidium can travel directly into the water source putting consumers at risk of illness.
In 2007, the Institute of Geologists in Ireland (IGI) published ‘Water Well Guidelines’ to provide guidance on drilling wells for private water supplies and set out best practice on water-well construction. Building on these guidelines in 2013, the EPA published ‘Advice Note No. 14: Borehole Construction and Wellhead Protection’. The latter were published in response to EPA observations of poor construction, finishing and protection of boreholes noted during audits of public water supplies originating from groundwater. The Advice Note sets out the best practice for the design, construction and protection of a drinking water supply borehole. The Advice Note is in three parts, which include details of:
- How groundwater changes with depth and how a borehole works;
- The best practice for design and construction; and
- A checklist and methodology for assessing the construction and protection of an existing water supply borehole.
The purpose of this Advice Note is to inform and instruct all to apply the IGI Guidelines when assessing the construction of existing drinking-water supply boreholes, and also apply the Guidelines when commissioning the construction of new boreholes. The final section of this Advice Note provides a combined desk- and field-based methodology to determine whether an existing water-supply borehole is drawing upon shallow groundwater, as well as deep groundwater. These two documents provide best-practice guidelines for water wells and should be used when constructing both public and private water supplies.
RISKS TO WELL-WATER QUALITY
To assist private well owners, the EPA is providing easy-to-use information on its website explaining what well owners should do to protect their health. The information includes a short animation (in English and Irish) to explain the risks to well-water quality and the simple things that can be done to reduce the risks.
A ‘Protect your Well’ assessment app is also available from the EPA website. Well owners can assess whether their wells are at risk in under ten minutes using this simple app. It provides well owners with tailored advice on how they can reduce the risk of contamination in their well.
Well owners are being advised to get their water tested at least once per year for microbiological contamination, ideally after heavy rainfall as this is when the supply is most at risk. If the results of testing confirm that contamination is present, well owners will need to take steps to protect their well (e.g. fencing the source or preventing surface water from entering the well).
However, if these measures are insufficient to prevent contamination (e.g. in karst areas where groundwater is heavily influenced by surface water), well owners will need to consider treatment based on the raw water quality. Treatment should include disinfection as a minimum but may require additional treatment where, for example, hard water or elevated levels of iron or manganese are present as these can affect the performance of disinfection systems such as UV.
The animation, web app, an infographic and general information for the householder about private wells are available on the EPA website.
Householder Information on Private Wells.
Private Well Assessment Web App – link to web app
‘Here is what you can do to make sure you well water is safe and secure’ – animation (available in both English and Irish).
Infographic (available in both English and Irish).