Northumbrian Water plans to replace the water treatment works at its sites in Otterburn, Rochester and Byrness, starting next month.
The investment will help to protect and improve future water supplies for people in the area.
Work will begin at Otterburn first, with Northumbrian Water′s supply partners Mott Macdonald Bentley (MMB) moving on to the site in April.
Work will then be carried out at Rochester and Byrness in April the following year.
Construction is expected to last up to one year in all three sites, with Otterburn complete by 2020 and Rochester and Byrness complete by 2021. The existing works will be demolished once each site is successfully commissioned.
Once they are operating to their full capacity, the works are expected to treat a total of 450,000 litres of water every day.
Northumbrian Water′s Project Manager, Hedley Young, said: "This work is part of a wider investment programme, to make sure that our customers have clean and great tasting tap water.
"The new treatment works will be built next to the existing works at each site, but they′re going to be bigger and better. They′ll use cutting-edge technology and systems to treat water to the highest quality and will be much more efficient.
"Customers shouldn′t experience any disruption to their water supply while we carry out this work, although they might notice more vehicular movement in the area."
Customers can follow the progress of the works at all three sites on Northumbrian Water′s Community Portal at www.nwlcommunityportal.co.uk and by following the link to the Otterburn, Rochester and Byrness WTW project page.