Manx Utilities says its waste treatment plant for Peel may not be finished until 2028 - but it'll start cleaning sewage next year.
Chair John Wannenburgh was replying to a question for written reply from Glenfaba and Peel MHK Kate Lord-Brennan about the timetable for the work.
In his response, Mr Wannenburgh said primary treatment screening should be ready next summer, while biological treatment will begin the following year.
He added earth-moving work, due to take place over the next six months, are most at risk of running behind.
Northern bus services to be raised in Keys
Ben out of service for maintenance work this week
Richmond Hill closed again tonight for work
October warmer and sunnier than usual, says Met Office
MHK queries cost of Liverpool awards trip
DOI says it has 20 empty public sector homes
Marquee plan submitted by Milntown Estate
Fire crews called to free driver from crashed car