75 % of domestic septic tanks inspected in Mayo last year failed the inspection.
That's according to a new report from the Environmental Protection Agency, which shows that, nationally, over half of domestic waste water treatment systems failed inspection, while almost one-quarter posed a risk to human health or the environment.
There are nearly half a million domestic waste water treatment systems in Ireland - mostly septic tanks, which can contaminate household wells with harmful bacteria and viruses if not built and operated properly.
The EPA report shows that six local authority areas had failure rates of above 75 per cent.
In Mayo, 93 inspections were carried out last year, with a 75% failure rate.
In Sligo, only one inspection was carried out, which failed, while in Roscommon, inspections were carried out on 20 septic tanks, with an 85% failure rate.
The EPA says local authorities must improve enforcement to ensure faulty septic tanks are fixed by householders, and grants of up to €5,000 are available for some categories.
In Mayo, between 2013 and 2020 367 systems failed inspection, of which 67% have been fixed.