High levels of a chemical compound, a suspected carcinogen associated with chlorine added to unfiltered water, have been found in Kerry's main regional drinking water supply in recent months.
Higher than acceptable levels of trihalomethanes (THMs) were found in the main water source itself at Lough Guitane near Killarney and other locations throughout the supply in October. Results for November were also high, although within current maximum legal limits.
THMs occur when chlorine, which is used to get rid of harmful bacteria, is added to unfiltered water especially from peaty soils.
Kerry County Council says it plans to introduce a €7 million filtration system at the plant which supplies half the county's drinking water, serving more than 50,000 people. A spokesman stressed that risks to public health were minimal and there was no cause for concern about the recent test results.
At present Lough Guitane has no filtration system to remove organic material prior to the injection of chlorine. Upper limits of 150µg/l (micrograms per litre) are currently set, but the EPA is asking local authorities to reduce this to 100µg/l by December 2008 in accordance with World Health Organisation guidelines for THMs in drinking water.
Compliance for THMs was in need of improvement and more stringent standards will apply in 2008 for trihalomethanes, the EPA warned in its most recent report on water quality.
Water samples taken from the Lough Guitane treatment showed contamination level of 178µg/l in October, the highest among a number of locations sampled. This had reduced to more than 103µg/l in November. High figures were also recorded for Abbeydorney and Castleisland.
THMs in very high doses are associated with rare intestine cancers, including kidney and bladder cancers in rats. They have also been associated with lower baby weights. No direct link with cancer in humans has been proved.
Ger MacNamara, senior executive in water services with the council, said high levels appeared to coincide with heavy rainfall and the tests would all have been taken on the same day.
Some €6.7 million was to be invested in the upgrading of the central regional water supply in 2007 which would include a filtration system at the plant, he added. A further €9.5 million is to be invested in the central water supply reservoirs.
Where filtration systems had been introduced in Templenoe and at Lauragh and water filtered before adding the chlorine to disinfect the water, water quality had dramatically improved and THMs had been reduced.
The council would like to see filtration in all of its schemes, Mr MacNamara added, as this would make the addition of chlorine easier.