Over a fifth of septic tanks inspected last year were a risk to human health or the environment.
The Environmental Protection Agency says over 800 tests were carried out by local authorities in 2020.
54 per cent of the tanks failed, because they weren't built or maintained properly.
In Kerry, 52 inspections were required last year but due to COVID-19 restrictions just one tank was inspected and that failed.
Between 2013 and 2020, 208 systems in Kerry failed inspections with 87% reported as fixed.
Noel Byrne, from the EPA, says there's a danger to public health in some cases.