The utility says it "was an option that Irish Water hoped could be avoided"
Details of water restrictions for Wicklow and Dublin have been confirmed.
It comes in a bid to protect water supplies amid the ongoing dry weather.
Irish Water says the night-time restrictions will be in place between 10pm and 5am from Monday for multiple areas across Dublin, as well as Bray in Co Wicklow.
Water pressure will be reduced during those hours, but there will be no loss of supply.
However, the utility is warning that some customers on high ground and in remote areas may see their supply 'reduce to a trickle at the kitchen sink'.
Low-night time pressures may also be experienced by those in multi-storey buildings, depending on individual water systems.
The restrictions will be in place for at least a week.
Irish Water's Kate Gannon explained: “Introducing restrictions was an option that Irish Water hoped could be avoided because of the inevitable impact on homes and businesses. The decision to lock down the restrictions to these areas was not taken lightly.
"If any customers are being adversely affected can they please call the Irish Water Customer Care line on 1850 278 278 and this will allow us to identify any areas where an undue impact is being felt.”
She added that the utility will 'continue to monitor the situation'.
Around two dozen other ares around the country are already experiencing restrictions, while a nationwide hosepipe ban remains in effect.
It comes as Met Éireann extended its status yellow drought warning until at least Wednesday, despite forecasts of "small rainfall amounts" over the coming days.
You can find a full list of the areas affected by the new water restrictions below: