The Environmental Protection Agency (EPA) has released a report on Tuesday which shows that human and animal waste was found in 60 private water suppliers.
Around 20% of the population's drinking water comes from private suppliers.
The number of supplies monitored in 2016 remained inadequate, with E. coli testing not reported for 809 private water supplies.
The report shows that private water supplies - which serves over 7,000 people in the country - are at greater risk of being contaminated.
"Local authorities must use their enforcement powers to ensure that action is taken where water quality issues are identified in private supplies," said Darragh Page, Programme Manager of the EPA’s Office of Environmental Enforcement.
"While there was an increase in enforcement by local authorities in 2016, only nine local authorities carried out audits during the year."
The full report titled 'Focus On Private Water Supplies 2016' can be found here.