The Churchfield Reservoir was built in 1982 and provides water to over 40,000 people on the northside of the city.
Structural issues were identified in 2018 which necessitated the removal of the old roof.
A 350-tonne crane is currently on the site close to Kilmore Road Lower installing the new roof.
Uisce Éireann say the project, which began in November, should be completed by September.
