Dublin and the surrounding midlands region are too dependent on the River Liffey for their water supply, according to Uisce Éireann.
CEO Niall Gleeson is expected to tell the Oireachtas Committee on Housing this afternoon that the Liffey, which is the main source of water for over 1.7 million people, is vulnerable to both drought and contamination.
A new supply for the region is urgently needed from the River Shannon, the state body has said.
Uisce Éireann believes that by 2044 the Eastern and Midlands region will need 34% more water than the current system provides, necessitating an upgrade.
The water company wants the Water Supply Project for the region to proceed as soon as possible to ensure Dublin, Meath, Kildare and Wicklow have a secure water supply.
The Water Supply Project would see water piped from the Shannon to a reservoir at Peamount in Dublin, servicing along the way as well.