A senior scientist with the Environmental Protection Agency has called on householders to take action to prevent leaks from their septic tanks.
The EPA inspected over 2,000 septic tanks and other domestic waste water treatment systems in 2017 and 2018.
Speaking on RTÉ'S News at One, Noel Byrne said that there was a 48% failure rate for these inspections.
Mr Byrne said that half of the failures were down to construction issues, with the other half due to maintenance issues.
He said a malfunctioning septic tank poses a risk to people's health and to the environment.
In particular, he highlighted the fact that households that have both a septic tank and their own water supply can be at risk of consuming contaminated water.
"A lot of this resides with the householder saying they are protecting their own health, their families, their neighbours and the environment," he said.
Mr Byrne said that householders should look out for any leaks or ponding from their septic tank, particularly in winter.
He added that a new grant scheme for septic tank works comes into effect this year and advised any householders who have issues with their tanks to contact their local authority about the scheme.