HOUSEHOLDERS are being enticed to pay the €50 fee to register their septic tanks with the offer of a €4,000 upgrade grant.
The Department of the Environment warned only applications from those who have registered by February 1 will be accepted.
So far 290,000 people – an estimated 58pc – have now registered.
The Census showed there are around 497,000 septic tanks or waste water systems in the country.
A maximum of €4,000 will be available for households on incomes of less than €50,000. Those earning between €50,001 and €75,000 can apply for a maximum of €2,500.
Environment Minister Phil Hogan said most of the deficiencies with septic tanks are "likely to be remedied by routine maintenance through regular emptying.
"Those tanks that are not working properly may be polluting groundwater and contaminating our drinking water supplies and must be remediated," he warned.
The minister said grants will only be available to householders whose system has been inspected by a local authority and been found to need improvements.
Mr Hogan urged householders to ask anyone calling to their door for identification.
Roscommon South Leitrim TD Denis Naughten said an analysis in Co Cavan had shown the grant should cover the upgrading of most septic tanks – with the average cost amounting to €2,500.
But he called for proper regulation to avoid vulnerable householders being "exploited by unscrupulous contractors".
The Irish Farmers' Association's (IFA's) environment spokesman Harold Kingston householders should be given every opportunity to register before the deadline.
People have been urged to register their septic tanks online at protectourwater.ie, by post on council forms or through local authority offices.