Irish Water is to lower the pressure in the greater Dublin area at night to conserve supplies.
The utility says it can sustainably and safely produce 610 million litres of water per day.
But in the past 24 hours, it claims this reached 615 megalitres.
"This level of demand meant drawing from treated water storage to maintain full supply", the company says.
"This option can only be maintained for a limited period of a few weeks.
"This record level of summer consumption is also depleting raw water reserves needed for the coming months."
Its Drought Management Team is meeting daily and monitoring water supplies.
It says the lowered night time water pressure levels for the capital "will not impact businesses but will assist Irish Water managing demand more effectively."
'At risk' water schemes
Nationally, it has identified 100 water supply schemes around the country that are at risk.
Customers in Kilkenny, Longford, Athlone, North Galway, Louth and Kerry have already experienced restricted water supply and outages in some cases.
Currently almost 4,000 customers are impacted.
Some areas in Cork, Wicklow, Limerick, Kilkenny, Carlow, Tipperary, Clare, Mayo, Sligo, Donegal, Galway, Roscommon, Laois, Limerick, Kerry, Waterford and Offaly have been identified as being at risk.
The utility has also been liaising with farming groups.