Irish Water says demand for water in the greater Dublin area remains critically high.
Some households in Athlone, Kilkenny, Longford and north Dublin have already experienced outages.
Parts of Donegal, Galway, Limerick and Mullingar are at risk of losing supply.
It comes as temperatures are set to reach 30 degrees in some areas today and tomorrow amid the continuing heatwave.
In the past 24 hours, demand hit 603 megalitres - a small decrease of six megalitres compared to the previous day.
However, the current demand is still said to leave "almost no margin of supply over demand", with Irish Water able to produce an estimated 610 megalitres of water per day.
The utility's Kate Gannon said there is evidence of the public conserving water, and welcomed Dublin Bus' commitment to only washing their fleet every three days instead of every day.
We believe we can all make a difference to protect our natural resources. We’re enjoying the warm spell but it's having a big impact on water supplies. We will save 100 gallons of water per bus by washing our buses every 3rd night instead of every night #ConserveWater pic.twitter.com/pEuwVVpRsL
— Dublin Bus (@dublinbusnews) June 26, 2018
However, she stressed there is still "a long way to go" to reduce pressure on supplies.
She explained: "If the drought is prolonged, water restrictions would become unavoidable if demand does not continue to drop.
"Irish Water are appealing to the public to be continue to be mindful of their water usage. Every effort someone makes in their home or business impacts their neighbour and community."
Irish Water has reiterated its advice for conserving water - including taking short showers rather than baths, and to avoid using hoses to water gardens or wash cars.
