The upgrade on Clyde, Creyke and Maidstone Rds, Ilam, is being carried out in three stages and is scheduled for completion in mid-2026.
Minor on-site preparations began at the end of August with the major work set to ramp up over the coming days.
"We are installing new, bigger pipes to help meet increasing demands on our wastewater network generated by our growing city," said council head of three waters Gavin Hutchison.
"People may see our contractors on-site soon, as they prepare to start construction of a gravity main (in September).
"We understand this community has already been disrupted in recent months by other infrastructure and roading works happening in the area and apologise for these further necessary disruptions.
"It’s a big upgrade and we’re working on multiple stages at once to get it finished as fast as we can to keep traffic impacts as short as possible."
During this time one-way traffic and detours will be in place, as well as a 30km/h speed limit to keep workers, motorists, cyclists and residents safe.
"Commuters should expect delays and are asked to follow the detour signage and keep an eye out for changes in traffic management," Hutchison said.
The second stage of the upgrade will affect the east end of Maidstone Rd, with work also planned on Creyke Rd beside the Clyde Rd intersection. This is scheduled to start in August 2025.
The third stage will happen in early 2026 on Maidstone Rd at the western end between Ilam and Waimairi Rds.
Hutchison said contractor Dormer Construction will keep residents and businesses updated as the work progresses.
