The Environmental Protection Agency has said more needs to be done to ensure drinking water from private supplies is up to standard.
It said continuing risks to public health are not being properly tackled and has called on local authorities to do more to ensure the quality of water, consumed by thousands of people each day.
The agency's 'Drinking Water Quality' 2021 report covers over 380 group water schemes, along with more than 1,700 small private supplies (SPS) around the country.
These serve a combined total of around 260,000 people with drinking water on a daily basis.
But one in 20 small private supplies - to premises like pubs, restaurants, nursing homes or creches - were found to have E.coli contamination, indicating that the water being consumed had not been properly disinfected.
And while local authorities are charged with ensuring these supplies are monitored for compliance with standards, today's EPA report shows that over a quarter were not reviewed at all, meaning there is no data on the standard of water they provide.
The report acknowledges that the impact of the pandemic may have restricted efforts in this regard, but says that, even allowing for this, overall monitoring is not at the level it should be at.
The EPA is also concerned that there may be a number of unregistered small supplies and has called on councils around the country to ensure there is proper recording and enforcement of quality guidelines.
Private group water schemes, typical in many rural areas, fared slightly better when it came to compliance with E.coli standards. Seventeen were found to be in breach in 2021, compared to 20 the previous year.
But, in overall terms, the EPA said a 95% compliance rate for these schemes compares unfavourably with the 99.5% level of adherence for public water supplies.
In addition, 7% of all group water schemes had higher than acceptable levels of trihalomethanes (THM); these are a by-product of the treatment process, as a result of excessive organic material in the water source. They are formed when something like rotting vegetation reacts with chlorine, used to disinfect water.
The report points out that Ireland was referred to the EU's Court of Justice in 2020, over failures to properly address THM levels in 44 drinking water supplies.
It also highlights a significant underspend when it comes to assistance available to carry out infrastructural improvements on private supplies.
While the Department of Local Government's Multi-Annual Rural Water Programme provides financial supports for these works, over 60% - or €36m - went unused between 2019 and 2021.