Irish Water said it was "increasingly likely" a hosepipe ban would be required across the country, as demand for water surged by 20% and the drought worsened.
Sixteen of the utility's drinking water schemes are in drought and 38 are at risk of going into drought because of the warm weather.
Irish Water's Yvonne Harris said there was a record spike in demand in Dublin on Saturday, and that a similar situation was playing out across the country.
She said: "In dry weather, our own behaviour with regard to water usage changes quite dramatically. Last Saturday, there was an additional 30 million litres of water used in the greater Dublin area. That's the equivalent of the water usage of an extra 200,000 people.
"We're seeing this trend throughout the country."
The forecast remains dry across the country until at least Thursday, when patchy rain is forecast for many areas. Further showers and colder weather are forecast for this weekend.
Mayo recorded the highest temperature in the country yesterday at 27.1C.
Most counties saw the mercury hit the 20s, but Malin Head in Donegal was a cooler 16.8C.
Met Éireann is predicting highs of 27C today.