A major sewerage system expense is looming for Lake Hawea residents.
One of the items in the Queenstown Lakes District Council's new 2015-25 plan is the investigation and construction of an upgrade to the township's wastewater treatment system.
The plan includes a cost of $73,000 in 2022 and $5.65 million in 2023.
Council chief engineer Ulrich Glasner explained to the Otago Daily Times this week the Otago Regional Council's consent for the existing system would run out in November 2022, and it was likely ''more stringent'' conditions would apply to any new consent.
Mr Glasner said there were issues at times with the way treated wastewater was discharged from the existing system.
Over summer, treated wastewater was sprayed on to grass which was harvested for stock feed, and that system was working very well, Mr Glasner said.
However, during cold weather the spray system froze, and water then had to be released into a trench which eventually led to the Hawea River.
Mr Glasner said there were no health issues with the practice, but a better solution was required.
One of the two options the council was considering was replacing the existing ''pond-based'' system with a ''sequencing batch reactor'' treatment plant.
The reactor would be a smaller version of the one used at the council's Project Pure plant which processed Wanaka's wastewater, and the cost would be between $8 and $9 million.
The second option was to pipe all Lake Hawea sewerage to the Project Pure plant, at a cost of $5.6 million.
''We are looking for the most affordable option for the Hawea community,'' Mr Glasner said.
The capital cost of such upgrades normally fell on the community that received the benefit - in this case the residents of Lake Hawea, he said.
There was still debate over how the operational costs would be met.
Asked about the capacity of Project Pure to take wastewater from Lake Hawea, and also from other places such as Cardrona, Mr Glasner said reducing water usage would help.
''We are doing a water metering trial, and if we could reduce water use in the future it will give us some credit on the plant.
''Maybe in a year's time, when the water meter trial is finished and we have a better picture, I can give you an update.''
