Northumbrian Water said it was installing new equipment at its works to help slow down pipe corrosion and to reduce water discolouration.
The work will take place at sites including Broken Scar in Darlington, Mosswood in County Durham and Warkworth in Northumberland.
A spokesman said the work would be completed early next year.
The work will not disrupt water supplies, the spokesman added.
More than £3m is to be spent upgrading four treatment works in the North East in a bid to improve water quality.