Donegal County Council is urging people with septic tanks and other similar systems to register them as quickly as possible.
The council is stressing while February next year is the deadline for registration, the reduced fee of five euro will only be available until the end of next week.
In a statement, Donegal County Council says owners of septic tanks or other domestic wastewater treatment systems are required to register their systems with their water services authority - currently the local authority. That may change when Irish Water is established.
A once-off registration fee of €50 is payable, but a reduced fee of €5 is in place until Friday week, September 28th.
The closing date for registration is February 1st next year, with registration to be renewed every five years. The will, the council says, be no charge for re-registration.
Registration and payment can be done on-line at www.protectourwater.ie, or in any of the six public services centres in the county.
Payment can also be made by post, with application forms in council offices, libraries and Citizens Advice Centres.
There has been substantial opposition to the registration requirement, with opponents pointing out that millions are spent on public schemes in towns and urban areas, as well as fears that substantial upgrading costs may be incurred after tanks are inspected.