Cavan and Monaghan has some of the lowest failure rates for septic tank inspections.
Across the country, half of septic tanks failed inspections last year, according to the Environmental Protection Agency.
A new report has raised concerns about delays in fixing faulty tanks, which can affect people's health and the environment.
The main reasons for the failures include structural defects, and a lack of maintenance.
There was a 32 per cent fail rate in Cavan, and 44 per cent in Monaghan.
Cavan and Monaghan had an 80 and 79 per cent fix rate respectively for 2021.