Minister for the Environment Phil Hogan has said some financial help would be available for people whose septic tanks are found to need significant upgrading after inspections begin next year.
However, Mr Hogan said he believed most problems would be resolved by de-sludging tanks, which on average would cost between €100 and €150.
He also said the approach of inspectors would be risk-based and that not every septic tank in the country would be inspected.
Mr Hogan said yesterday the fee would be reduced from €50 to €5 for three months as an incentive for people to register early.
But he ruled out any similar reduction in the €100 household charge where registration is running at around 5%.