Tiaki Wai is spending $150 million dollars to fix a foul stench that's plagued a Lower Hutt community for years.

But the water agency is warning of more odour over the next two weeks during works for its major, years'-long project replacing sludge dryers at the Seaview Wastewater Treatment Plant.

Residents have spoken out in previous years about the rotten, vomit-inducing smell caused by the plant, which brought on headaches for some, and prevented people opening their windows and doors.

The waves of stink were caused - in part - by current sludge dryers which were old and prone to breakdowns.

The dryers are "massive" pieces of equipment which remove water from sludge and compact it before it is trucked to the dump, Tiaki Wai operations manager for treatment and control systems, Jeremy McKibbin, said.

"When the dryer broke down, what it meant was that we weren't able to remove enough of the actual biological matter from the process and dry it and send it to landfill.

"And so when that biological process becomes unbalanced, it stinks.”

It is an all-too-familiar scenario for neighbouring business owner Jaysen Eveleigh.

"It gets down your throat, and it just makes you feel sick. You can't be outside, you have to walk inside."

Downer staff are constructing the building that will house the new dryer at the Seaview Water Treatment Facility.

Eveleigh ran On Road Logistics across the road from the plant and said while the stench came and went - when it's bad, it's still bad.

He had endured it frequently this year and could not understand why the area had to keep suffering from it.

Alex Beavis, who lived on the nearby Bell Rd, said the smell was less frequent than it was two years ago.

But at times the "portaloo" stink still wafted over when she was sitting outside with visitors.

"It makes me angry, because we end up going inside ... it's embarrassing."

McKibbin said the two new electric dryers - being manufactured in Germany - had a built-in odour management system. The project involved 19 local businesses and was on track to be finished by December next year.

The cost included 3000 stone columns for seismic strengthening and construction of a new building to house the dryers, new conveyor belts and boilers.

An $8 million project, completed in 2025, focused on odour treatment of the plant's milliscreen area - where foul air is scrubbed through carbon filters.

"My message to the community is that there is a significant amount of investment underway now to avoid a repeat of the problems that we had in recent years that really did impact the community," McKibbin said.

A recent message from the agency on social media warned the community could face the smell again between October 9 and 18 due to replacement works.

Lower Hutt Mayor Ken Laban described the stench as "dreadful", "unacceptable" and at times "almost unliveable".

"Clearly something had to be done ... there's going to be some pain in the meantime. But when it's fixed people get to live in an environment they feel comfortable in."

Laban said the $150 million project was an agreement Tiaki Wai took over from Wellington Water and Hutt City Council.

He said he had "100 percent confidence" Tiaki Wai would fix the plant by December 2027.