Many private water suppliers are failing to ensure their water is safe to drink.
A new report from the Environmental Protection Agency (EPA) has found that one-in-20 private water supplies in Ireland does not meet safety standards.
That is compared to one-in-200 for public supplies.
On Newstalk Breakfast, EPA programme manager Noel Byrne said suppliers can access State funding to improve water quality.
"The water in private supplies hasn't improved in recent years," he said.
"What we're seeing is one in 20 contaminated wells with E. coli continuing for the last couple of years.
"Last year it affected 6,000 people; and that's compared to maybe one in 200 for public supplies.
"We're quite a difference there between the private supplies and the public supplies.
"The report also [found] for the 1,700 private supplies, over a quarter of these were not monitored - which provides really no assurance to the quality how safe it is to consume".
The EPA found one in that local authorities are not monitoring over a quarter of small private supplies for E. coli - and there may be many more supplies which need to be registered with the local authority.
Private water supplies serve around 200,000 people in rural communities - as well as some small private supplies such as hotels or schools.
In this sector last year, there were more than 50 Boil Water Notices in place for over 5,000 people.
Mr Byrne said the reasons for contamination could be down to necessary upgrade works.
"These are all independently owned and in many cases some of these can be old and need upgrade works," he said.
"Department funding is available there for it, but it's disappointing to see that 60% of that funding, which equated to €36 million over the past three years, wasn't used to address the supplies that are failing.
"It's up to suppliers to make sure their supply is safe to drink.
"If their infrastructure needs to be upgraded, use the funding that's available to make sure the supplies are safe to drink," he added.