Almost six out of every ten domestic septic tanks failed inspection last year, putting drinking water, wells and rivers at risk, the Environmental Protection Agency has said.
There are nearly half a million domestic wastewater treatment systems, or septic tanks, in Ireland.
They are used to treat wastewater where homes are not connected the public sewage system.
Local Authorities are required to inspect a minimum 1,200 septic tank inspections per year.
These inspections are generally targeted at areas where septic tanks present a pollution risk.
The majority are near rivers known to be at risk and in areas where domestic septic tanks are co-located with household drinking water wells.
Reasons for failure include operational issues such as inadequate desludging and maintenance, as well as structural defects including illegal discharges to ditches or streams, leaks, ponding, and rainwater ingress.
Faulty septic tanks can contaminate drinking water wells with harmful bacteria and viruses.
Also, people may be exposed to wastewater if it surfaces in gardens or runs off into ditches and streams.
There are also risks to the environment because excessive releases of nitrogen and phosphorus from faulty septic tanks can cause pollution in receiving waters.
This has been identified as a problem in 148 water bodies around the country.
Inspections of Domestic Wastewater Treatment Systems are carried out by Local Authorities.
Last year they conducted 1,466 of these inspections. The number that failed was 863, or 59%, with a significant number identified as a risk to human health and the environment.
The report says three local authorities, Fingal, Donegal and Wexford did not carry out their full quota of inspections last year and need to double up inspections to make up for those shortfalls this year.
It also says that 84% of septic tanks that failed inspection last year were fixed by the end of 2025, while the number of advisory notices unresolved for longer than two years fell noticeably to 442, down from 252 in 2024.
This improvement was aided significantly by the availability of the enhanced government grant for the remediation of septic tanks which was increased from €5,000 to €12,000 in 2024.
However, EPA’s Office of Radiation Protection and Environmental Monitoring Director Pat Byrne said more consistent and sustained enforcement is needed across all local authorities to ensure that faulty septic tanks are fixed as soon as possible and that public health and the environment is protected.
Inspection failure rate 'worrying'
EPA Programme Manager Noel Byrne said: "Regular checks and routine maintenance of septic tanks by homeowners can prevent minor issues becoming major problems, helping to protect their family’s health and the environment."
Speaking on RTÉ's Morning Ireland, he said that people need to check their septic tanks for the sake of their family and the environment.
Mr Byrne said the fact that six out of 10 water treatment systems have failed septic tank inspections was "worrying statistic".
"They can pose risk to drinking water wells and to our rivers and streams, so they must be resolved by homeowners," he said.
Mr Byrne explained that there are two key causes of failures, issues in construction and maintenance.
"The first thing, there is construction. So, you can have such a thing as a leak from a tank. But local authorities have found many cases, there's been pipes going out from septic tanks into rivers, which really isn't just acceptable in this day and age.
"On the other side, then, it's simple maintenance issues, such as emptying your tank, which would be better known as de-sludging. But that's a simple step that homeowners can do.
"Because if you don't do those simple steps, actually things can become worse. If you don't de-sludge, that can damage a percolation area.
"So something that might cost you maybe three or four hundred euros to do once every three or four years, could turn into a much more significant cost if you damage your percolation area."
