Widespread rationing of water will hit busy pubs, hotels and nightclubs
Cut offs hit at the height of tourist season
Pubs, hotels and nightclubs face having have no water at night at the height of the busy tourist season.
Widespread restrictions to be introduced from Monday night across Dublin city centre and suburbs and parts of Wicklow could lead to loss of supply for businesses without a back-up in place, Irish Water said.
While homeowners and businesses can expect to see reduced pressure when the restrictions hit between 10pm and 5am, there should be enough to keep water flowing from the kitchen tap on ground floors.
However, properties on higher ground or at the edge of the network can expect to see supply reduced to a trickle, and Irish Water said it could not rule out customers losing supply.
More than 30 locations in an area stretching from Bray in Wicklow to Finglas on Dublin's northside and Lucan to the west will be affected.
"What we're trying to do is maximise the amount of water we can save while minimising the impact on homes and business. It's very hard to do," corporate affairs manager Kate Gannon said.
"For general customers, some on high ground and remote ends of the network will experience low pressure but shouldn't experience a loss of supply.
"For non-domestic customers, the practice is to have 24 hours' storage on site. If you're in an older building, it may be harder for them. We appreciate not everybody has that. We cannot promise that everyone will feel nothing."
More than 25 supplies across the country are already hit with night-time restrictions, including Athlone in Westmeath and parts of Galway city.
Unless there is sustained rainfall, additional measures including day-time restrictions are likely to be imposed.
The Dublin restrictions were needed to protect future water supply and "avoid widespread outages in the autumn", it said.
Areas around hospitals will not be affected, and the restrictions were timed to end at 5am to allow water pressure to build back up and avoid impacting on families. "We expect supplies to be back by 6am or 7am because we don't want people impacted in the normal hours," Ms Gannon said.
While the hosepipe ban, coupled with conservation efforts from the public, had saved more than 40 million litres a day, it was not clear as to how much additional water would be saved during the restrictions.
"We do have to take this extra step because we're trying to catch up on the demand over the last number of weeks," she added. "We're hoping the changes people have made are ones they can sustain over time. We hope to gauge how much we can get back."
Supplies affecting more than 700,000 people across the country are either in drought or at risk of drought, and have been given a 0 to 5 risk rating, with levels 0 to 3 seeing no day-time restrictions.
All affected areas in Dublin are subject to a Level 2 restriction. If level 3 restrictions were imposed, they would be in force from 10pm to 5am, and extended to 9pm to 7am as required.
Levels 4 and 5 would affect supply during the day, with rolling shut-offs from 10am to 4pm, and 9pm to 7am.
"We would hope to avoid those at all costs," Ms Gannon added. "The weather is outside of our control and it's not changing. It's a real worry.
"We've had 40 days of little or no rain. We wouldn't be taking this step if we could avoid it."
Anyone with supply issues should contact Irish Water on 1850 278 278.