The first to get under way will be the new Alexandra water supply upgrade, estimated to cost about $8.5 million, which is due to begin in July and should be completed by December 2017.
The upgrade is needed to address residents' concerns about water quality and also to meet national drinking water standards.
The second is the Cromwell wastewater treatment upgrade, estimated to cost about $10 million, and construction is to be completed in 2019.
The upgrade was described by Central Otago deputy mayor and Cromwell Community Board chairman Neil Gillespie last year as ''the most important infrastructure project'' for Cromwell since the redevelopment of the town about 30 years ago.
An upgrade is needed to qualify for consents from the Otago Regional Council to discharge treated wastewater into Lake Dunstan.
At a meeting last week the council considered the processes needed to deliver the two projects.
Cr Steve Battrick said both were the culmination of a ''long journey'' and hard work.
Council infrastructure services manager Jon Kingsford said the exact timing of compliance with the national drinking water standards was yet to be determined but that was the goal and work would be carried out in stages towards that over several years.
The project will include a new bore field intake, a treatment facility, a large-diameter falling main and a reservoir.
The new water supply could provide potable water to Alexandra, Clyde and the rest of the Dunstan basin, he said.
Separate contracts for design and build were favoured by Mr Kingsford and that method was approved by the council.
For the Cromwell wastewater treatment upgrade, he preferred a design, build and operate option of delivery, and the council agreed.
Mr Kingsford said the project would be challenging as the existing system would have to operate while the new one was constructed and commissioned.
He recommended the contractor take over operating the plant up to a year before construction began, so they could see how its operation varied throughout the seasons.
Councillors debated how many elected representatives should be on the group which oversees the projects.
Chief executive Leanne Mash said it was important Mayor Tony Lepper be on the group and said it would be good practice to have two more elected representatives as well, because ''we're talking a big chunk of money [for the projects]''.
Cr Neil Gillespie queried whether there was a need for three elected members but agreed the Cromwell Community Board should be represented on the wastewater project group.
