€21.7m is going to be spent improving the water supply for 65,000 buildings in North Dublin.
The works, which will start in February, will mean less unplanned outages around Howth, Malahide and Balbriggan.
Irish Water says the upgrade will include new pumping stations and fifteen kilometres of new trunk water mains.
The project, which isn't due to be completed until the end of 2020, will also ensure the system can meet future demands for housing and business.
William McKnight from Irish Water, said the upgrade "will ensure that customers in Howth, Malahide and Balbriggan will have a more reliable and secure supply which will result in fewer disruptions to their water supply".
