Two thirds of household septic tanks inspected by local authorities last year were found to be faulty.
There was a 62 per cent failure rate in Roscommon and a 60 per cent failure rate in Longford.
There was a 100 per cent failure rate in Leitrim, with all four of the tanks tested not meeting standards.
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The Environmental Protection Agency says the failure to fix faulty septic tanks is a risk to human health and the environment.
Noel Byrne from the EPA explains the reason for many failures.