It will improve the quality of water for over 60,000 people.
Upgrade works worth €8m to a Westmeath water treatment plant are now complete.
The Portloman Water Treatment Plant provides water to 63,000 people in the Mullingar area.
The aim of the project is to have a reliable water supply for homes and businesses in the region.
Works included replacing membrane filters and optimising the treatment process, as well as installing solar panels and high performing energy efficient pumps.
John McElwaine, Programme Manager with Uisce Éireann says "This project is of vital importance for residents and businesses in Mullingar and the surrounding areas. The completion of these works now safeguards the water supply in Mullingar presently and into the future."