Up to one in four households with waste water systems have still to pay their septic tank charge.
New figures show that 125,000 have still to register for the new inspection scheme, the deadline for which passed at the start of the month.
City councils and some of the country’s larger county councils are the worst offenders when it comes to residents paying the waste water charge.
Figures from the Department of the Environment show 376,451 had registered for the charge out of an estimated 500,000 properties with waste water treatment systems before the February 1st deadline.
Only households who registered their systems by that date are eligible for financial support if their system fails an inspection.
Kerry had the highest level of registrations at 99% with Dublin City having the lowest at 3%.