A nationwide hosepipe ban comes into force this morning.
Irish Water says supplies remain dangerously low and it could take months for levels in rivers and lakes to return to normal.
Most of the country is in the grip of drought, with temperatures set to rise over the weekend.
Irish Water’s Kate Gannon said: "Our sources are precious, there will be little or no rainfall for the next 10 days and we want everybody to be more mindful of their usage.
"We are doing everything we can on the ground to maintain supplies and we'd ask everybody across the country to play their part too."