It comes as Met Éireann has issued a drought warning for the whole country
The hosepipe ban in the Dublin area could be extended to other areas where water supplies are under pressure.
Irish Water has announced the measure in response to the "unsustainable levels" of demand during the heatwave.
People in the greater Dublin area could face prosecution or a €125 fine if they do not comply with the ban, which will come into force on Monday.
The Dublin restriction will be in place until at least the end of July, but may be extended due to the dry conditions.
This morning, Met Éireann has issued a warning for the whole country - saying drought or near-drought conditions "will persist through the coming week".
DROUGHT WARNING— Met Éireann (@MetEireann) June 30, 2018
Drought or near-drought conditions will persist through the coming week.
Valid from Saturday 30 June 2018 10:00 to Friday 06 July 2018 23:59https://t.co/oOxITrsnvw pic.twitter.com/AW1b3yUkvl
Meanwhile, more than 100 supply schemes are at risk across the country, with restrictions - such as lowered water pressure during the night - already in place in various areas.
As the warm weather continues, the demands on water supplies is outstripping the supply in several areas around the country, including the Greater Dublin Area, with increased demand at 10% above normal or more. #ConserveWater #HeatWave— Irish Water (@IrishWater) June 29, 2018
Eamon Gallen from Irish Water says people need to conserve as much as they can.
He said: "We're encouraging people to please increase their conservation efforts.
"We've had great response from a lot of the public, and indeed a lot of our commercial customers. But we need people to save water now, so we don't face restrictions throughout the late summer and autumn."
He added: "At the moment [the hosepipe ban] applies only to the greater Dublin area - but we'll continue to examine the over 100 at risk schemes for possible application of similar water conservation orders."