The overall quality of public water supplies is satisfactory, with 91 per cent of samples tested being acceptably within safety limits, says the Environmental Protection Agency.
However, the overall quality of group water schemes continues to be unsatisfactory, according to the EPA's report on The Quality of Drinking Water in Ireland for last year.
The EPA estimates that local authorities produce and distribute more than 90 per cent of drinking water.
Most of the remaining supply comes from group water schemes, where water is distributed by private individuals or committees.
Only 60 per cent of group water schemes, which supply about seven per cent of all drinking water, were found to be within acceptable safety levels.
Monitoring of drinking water by county councils and corporations increased by a third on 1999, which the EPA said was a significant increase.
In 2000, local authorities undertook 142,000 individual tests on over 2,500 different drinking water supplies.
In Ireland, the most common concerns are about water contaminated by sewage or animal slurry.
The presence of this pollution can be determined by a test for bacteria called coliforms, some of which, faecal coliforms, originate in human and animal waste. Others coliforms are found in the soil.
For public water supplies, the overall total coliform compliance rate in 2000 fell marginally to just above 90 per cent.
This figure was brought down by low compliance levels in public water supplies in north Cork, west Cork, Co Sligo, Waterford county and Wicklow.
Group water schemes had an overall total coliform compliance rate of almost 60 per cent, down 4 per cent on last year.
Nine local authorities had a total faecal coliform compliance rate of less than 50 per cent: Carlow, Cavan, Donegal, Kilkenny, Louth, Mayo, north Tipperary, south Tipperary, Waterford county.
In addition, group water schemes had an overall compliance rate for faecal coliforms of almost 70 per cent, a compliance described as poor by the EPA.
Group water schemes in 10 counties had collectively a compliance rate for faecal coliforms of less than 75 per cent.
These authorities are: Cavan, Donegal, Galway county, Kerry, Mayo, Roscommon, Sligo, Tipperary north, Tipperary south and Wicklow.
The authority gave a county-by-county breakdown, and mentioned problems in places such as Sligo and Kilkenny city. And in Fingal: there were "objectionable odour and taste problems" in the area's two drinking water sources, .
In Sligo the "bacteriological quality of the drinking water quality must be regarded as less than satisfactory", the EPA said. In Kilkenny city more than half the samples taken from the Troyswood scheme exceeded the aluminium standard.
Public water supplies had a faecal coliform compliance rate of almost 97 per cent.
The quality of group water schemes is expected to improve with the allocation of €533 million under the National Development Plan, said Mr Gerard O'Leary, senior scientific officer with the EPA.
The Chairman of the National Federation of Group Water Schemes, Dr Jerry Cowley, welcomed the report, but called for increased funding under the National Development Plan to ensure group water schemes are brought up to standard for producing quality water.