The failure of a single main pipe providing water to Dublin could leave the capital in "big trouble", the head of Irish Water has warned.
Large parts of the city's sewer system have not been inspected in 50 years, and the flow of waste water from the north to the south of the Liffey would be stopped if a pipeline collapsed, managing director Jerry Grant added.
The utility needed a guaranteed source of funding over at least a five-year period, otherwise it would not be held "accountable", said Mr Grant.
There is a need to spend €13.5bn over the longer-term upgrading the network, but the Government has yet to commit to funding beyond next year.
"We have to work on the basis that our five-year plans, which are approved by the Government, will attract committed funding at the appropriate time," said Mr Grant.
"If we say we're going to deliver all these things and outcomes and the money doesn't come through, there's really no accountability on us.
"If the funding falls off, it damages the programme but it also damages your ability to deliver because the supply chain loses confidence.
"We're trying to develop a supply chain to match our needs. If we can't follow through, that supply chain will disappear and go to other things."
Among the major concerns are the failure of "critical assets", many of which were built by the British and have not been inspected or upgraded in decades.
"Everybody knows about the Vartry system," said Mr Grant.
"We would be very anxious still about the pipeline between Ballymore Eustace and Saggart. We have a pipeline to Swords that fails on a regular basis.
"We're going to replace that, and the contract will start before the end of the year. There are many other examples."
Failure of the Vartry Tunnel, which links the treatment plant in Co Wicklow to the Stillorgan reservoir, would result in 100,000 people in north Wicklow, including Bray and Greystones, being without water.
If a pipe from the Ballymore Eustace drinking water treatment plant in Co Kildare fails before planned additional storage and a back-up pipeline is constructed, it would leave the capital in "big trouble".
If repairs took longer than two days, there would be "considerable" water restrictions in the city, Mr Grant said.