Just over 20 per cent of households have still not registered their septic tanks and waste water systems, although the deadline expired last on February 1st.

A statement issued by Environment Minister Phil Hogan thanked the 400,000 households who have registered, and appealed to those who have not signed up to do so.

He also confirmed that inspections will begin this summer - and that housholders who haven't registered will be liable for a fine of up to €5,000.