People in all areas of Dublin are being asked to use as little water as possible over Christmas.
Data shows demand has been increasing in recent weeks, and is now at a record high for this time of year.
Irish Water is warning that, unless people start to use less, the supply may have to be restricted.
The current increase in demand is higher than any previous year and is 10 million litres a day, which is enough water to fill Liberty Hall.
Dublin has less spare water to play around with, as works continue to fix issues at the Leixlip Water Treatment Plant.
John O Donoghue, Irish Water, admitted "there is currently no headroom in the system".
"Safe, clean, treated water is not in unlimited supply", he warned.
Dubliners are being asked to turn off the tap while brushing teeth and shaving.
Other suggested ways to conserve water include keeping a jug of water in the fridge, instead of running the tap until it's cold.
Irish Water is also encouraging customers to report leaks to 1850 278 278.
