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."
Ms Gannon explained how the hosepipe ban will be enforced, saying: "Contact the individual, usually by going out to check if the usage is included in the water conservation order, probably knocking on the door and saying 'are you aware there is a water conservation order in place, are you aware that these activities aren't allowed?'
"And in the vast majority of cases, the individual is simply unaware that the ban is in place and they shouldn't be doing it."