The main source of Dublin's drinking water will diminish during the next few decades as the city's demand for water rockets.
Irish Water says the volume of water available from the River Liffey will fall by 50 million litres of water a day by 2050, while Dublin's thirst will grow by up to 330 million litres.
"We have a climate and biodiversity emergency and that's becoming very real," said Sean Laffey, Irish Water's head of asset management.
"We're having a second drought in three years and our studies indicate, for instance, that by 2050 there'll be 50 megalitres a day less available in the Liffey for Dublin."
The Liffey provides more than 80pc of all of Dublin's daily water needs, but that means 40pc of its waters are extracted every day to serve the city.
"If you over-abstract from a water body at particular low flows you can very quickly do irreversible ecological and environmental damage," Mr Laffey said.
The warning, delivered to the Environmental Protection Agency's (EPA) national water conference, came as Irish Water confirmed drought conditions have worsened since the start of the hosepipe ban.
Despite heavy rain showers in many parts of the country over the past week, water levels in most rivers and lakes remain under stress.
From the time the likelihood of the ban was flagged on June 1 to the start of the ban a week later, the number of water supplies in drought rose from 16 to 27 and the number at risk of drought from 38 to 50.
By last weekend the figures had risen further to 35 and 52, and since then they have increased to 38 and 58.
Further showers and some prolonged spells of rain are forecast over the coming week but they come after an almost total absence of rain from mid-March to early June, a period that was the driest since 1850 or even longer in some places.
"Unfortunately short periods of rainfall, such as those we have experienced in the last week, are not sufficient to return raw water sources to normal levels," an Irish Water spokeswoman said.
"We are keeping the situation under continuous review and are liaising closely with other key agencies such as Met Éireann, the OPW, the EPA, among others and if the situation improves we will consider lifting the water conservation order. However, any change is unlikely in the short term."
Irish Water has proposed developing an alternative long-term water source for Dublin by piping supplies from the Shannon, a massive and controversial project that is currently being reviewed by the Commission for the Regulation of Utilities.
The new draft programme for government is non-committal on the idea, saying only that the coalition would "fully consider the review".
Meanwhile, recent heavy downpours of rain have caused problems for the country's water infrastructure.
Pollution risks from storm water overflows have closed beaches at Sandymount and Portmarnock, in Dublin, and the swimming area at Ballyallia Lake, Co Clare, while overflowing sewage plants have closed Dollymount in Dublin and Clonea in Waterford.
The beaches are to remain closed for three to five days.