The Government has insisted efforts are being made to ensure the safety of drinking water after a report found nearly a quarter of all water from private schemes is unfit for drinking.
In a report on drinking water quality in the State in 2005, the Environmental Protection Agency found there is insufficient monitoring of public water supplies and group water schemes.
It said compliance among private group water schemes with E.coli standards fell to just 77.5 per cent in 2005, meaning a quarter of all water from these schemes is unsuitable for humans. E.coli contamination arises from human or animal waste.
The EPA described the performance of the private schemes as "worrying".
Minister for the Environment Dick Roche accepted there were concerns but insisted water hygiene standards were being improved.
"My department, through the local authorities, is investing hundreds of millions of euro on upgrading these schemes. Very rapid progress is being made all over the country, and this will be reflected in future EPA reports," he said.
The EPA said supplies to major cities were satisfactory, particularly in the Dublin, Cork, Limerick, Galway and Waterford areas.
But the agency found some 232 out of 640 private group water schemes monitored were contaminated with E.coli.
The EPA found that 65 per cent of private group water schemes in Cavan; 60 per cent in Kerry; 82 per cent in Leitrim; 67 per cent in Donegal; and 54 per cent in Sligo were contaminated with E.coli at least once during 2005.
Nationally, the percentage of schemes contaminated with the bacteria dropped from 40.4 per cent in 2004 to 36.2 per cent in 2005.
Around 7 per cent of the population is served by private group water schemes, and a further 10 per cent is served by private wells that are not covered by regulations.