The project is being carried out by Irish Water.
Works taking place tonight are likely to affect water supply to Johnstown and its hinterland.
Irish Water is conducting stop testing from 11pm.
Kildare County Council says "customers may experience Low pressure, a total loss of supply of discoloration in the water supply"
Johnstown village, Kerrdifstown and Forenaughts may be affected.
The project is due for completion at 4am on Thursday morning.
It could take up to three hours for the system to refill and for normal supply to resume.