Around 4,000 customers in the Castlepollard area had been affected.
A boil water notice in Westmeath is being lifted with immediate effect.
The advisory was issued last Tuesday, the 1st to about 4,000 customers in the Castlepollard, Delvin, Collinstown, Coole, and Raharney areas.
A mechanical issue with chlorination at the Ballany Water Treatment Plant has been resolved and the disinfection process is operating normally again.
Irish Water and Westmeath County Council are thanking the community for their patience.