Inland and western counties are experiencing the best of today's weather.
Temperatures in many areas could reach 30 or 31 degrees, with similar temperatures forecast again tomorrow across Connacht.
A number of water schemes across the country are in a critical situation as the heatwave continues, with night-time restrictions imposed on the Ballyconneely Water Treatment Plant and on Inis Oirr, the smallest of the Aran Islands - water supplies in these areas are restricted between 11pm and 7am.
Across the region, reservoir levels have dropped and there's also extra demand on the system as people are using more water.
Irish Water is appealing to people across Connacht to conserve water during this hot spell.
They say demand has increased in particular in the Westport area and on the Lough Mask supply, and people should refrain from washing cars or leaving taps running, and report any leaks to Irish Water.