Irish Water is warning supplies in the Greater Dublin Region could fail after 70 days.
Levels remain under threat following the recent heatwave - with the hosepipe ban still in place around the country.
Meanwhile night-time water restrictions in the Greater Dublin Area will remain in place until the end of the week at the earliest.
Irish Water managing director Jerry Grant said people must continue to conserve water in the coming weeks.
“About the 10th or 12th of May we had 150 days of storage in Poulaphouca,” he said.
“It is an enormous source of water and it saves the city year in, year out.
“We used 80 days of that storage in 83 days – in other words, almost nothing was contributed to the storage in that period.
“We have about 70 days of usable water left for the Greater Dublin Area – 1.6 million people.
“We could be 90 days before that lake starts to rise, depending on how dry the autumn is.”
Irish Water has launched a new water conservation information campaign for August. The hosepipe ban is in place until end of the month. ‘Don’t rush to flush’ - their top tips are also on their website https://t.co/erpwRyAnr3 pic.twitter.com/hqUW7YHBw7
— Gail Conway (@Gailiana) August 2, 2018
Met Éireann recorded 63.9 millimetres of rainfall at Dublin Airport across May, June and July this year – significantly less than in the previous three years.
Last year, the forecaster recorded 172.1mm, with 149mm recorded in 2016 and 173.8mm recorded in 2015.
Meanwhile leakage from water mains pipes in Ireland is at 49% - making the country the worst performer in western Europe for pipe leakage.