Uisce Éireann says levels in treated water reservoirs are historically low.
It’s urging people across the country to conserve water during the warm weather.
A high temperature warning is in place for 13 counties until tomorrow.
Carlow, Cork, Kildare, Kilkenny, Laois, Limerick, Longford, Meath, Offaly, Tipperary, Waterford, Westmeath and Wexford are affected.
Meanwhile, a similar warning comes into effect tomorrow at 1pm for Clare, Cork, Galway, Kerry, Kilkenny, Laois, Limerick, Mayo, Offaly and Tipperary.
It will remain in place until 7am on Tuesday.
