Army units joined emergency crews volunteers and worried locals around the country as communities rallied in the face of rising flood waters.
Here are some of the worst flood hit areas.
About 200 people were evacuated from homes and businesses when the Suck burst its banks.
Schools were shut, the main Dublin to Galway road closed and all rail and bus services to Galway suspended for several hours.
Authorities were later forced to open a 26km section of the new M6 motorway to ease traffic pressure and create a cross-country route for motorists.
Residents were also warned to boil all water before drinking it while the Defence Forces deployed 20 soldiers with trucks and a flat-bottomed boat to evacuate families.
Local councillor Michael Mullins said parts of the town were under at least three feet of water.
“It’s horrendous,” he said.
“It’s really serious. There is going to be a lot of pain, hardship and inconvenience.
“A lot of people are very frightened and the water is still rising in the square.”
A family of five were airlifted to safety during an early morning rescue operation as flood waters surrounded their home.
An 87-year-old woman was among the occupants winched from the property in Kilbeacanty, near Gort, at 2.30am.
The rescue mission took an hour, with the Irish Coast Guard helicopter landing in a nearby floodlit GAA pitch.
The 300-bed Mercy Hospital was forced to move A&E patients from the ground floor to higher levels after a quay wall on the Lee collapsed spreading the floods.
Businesses in the city hit out at the ESB claiming officials failed to alert them after a decision was taken to open a dam further upstream on the river.
The Mercy, just yards from the banks of the Lee, was closed to new admissions and attempted to discharge those fit to leave and send others on to different hospitals.
Substantial flood damage was caused to a number of key buildings at University College Cork (UCC), which is now closed for at least a week.
Foreign Affairs Minister and local TD Micheal Martin praised the work army teams put in to help emergency teams battle the rising waters.
“It is important as the situation continues to unfold that people check on older neighbours to ensure they are safe and secure,” the minister said.
“In addition all warnings and advice from the Gardai should be heeded.”
Seventy soldiers were on the flooded streets manning six vehicles and three boats to bring people to safety.
UCC shut down with 14 buildings flooded and student accommodation.
“Unfortunately, most of the student buildings were affected by the unprecedented severity of the flooding,” a spokeswoman said.
“Further precautionary measures are being taken in relation to the likelihood of flooding re-occurring over the weekend.”
Cork city council has confirmed that water supply to tens of thousands of homes will be cut off for a number of days.
All of the northside of Cork city and the Douglas area in the south will be without water because of flood damage to the local water treatment plant. Temporary water tankers will be deployed.
Ambulance crews joined the Red Cross and the Army with jeeps and trucks to bring staff to work at Bantry General Hospital, the five Community Hospitals in West Cork and to Cork University Hospital.
In Mallow, however, for years one of the country’s flood black spots, relief works almost complete have kept the worst of the high Blackwater at bay.
But the river burst its banks further downstream in Fermoy, making the Fermoy Bridge, the Quays and the Tallow Road impassable.
The flooding forced the Supervalu supermarket and other shops to close for the day.
However, Flan Groarke, an engineer with Cork County Council, said water in the town was receding after floods peaked in the morning.
Fermoy residents were hoping heavy rains would miss the Blackwater catchment over the next 24-48 hours.
“Hopefully it won’t rain for the rest of the evening, we will need a lot of rain to come down from Kerry to be affected again
“We are on alert.”
Water levels in the lakes have risen almost 8ft with waves lapping around the edge of the Lake Hotel.
Niall Huggard, general manager, said he was forced to close its doors, evacuate 110 guests and shift period furniture to higher floors.
Cars also had to be pulled from a flooded car park with a tractor and trailer.
“We’ve never seen anything like this,” said Mr Huggard.
“We’ve got about 60 people carrying furniture from the ground floor to the first floor. We’ve girls that came on their days off rebooking guests.”
The N71 Killarney to Kenmare Road was also closed at Molls Gap.
Ennis town was hit by unprecedented floods with all but two approach roads closed.
Forty houses were evacuated as 20 members of the Defence Forces tackle flood hit streets.
A council spokesman warned: “Despite respite from the heavy rain of previous days, it is expected that tidal conditions will continue to pose a flooding threat.
“It is expected that further rain over the weekend will create additional flooding problems for Ennis.”
Roads across the county were largely “bad but passable” but old roads around Newmarket on Fergus, Ennistymon, Kilrush and Killaloe were under water with serious flooding around Broadford and Doon Lough.
All bridges in the town were closed, except one, as a swollen River Suir breached defences and left the quays under three feet of water.
Schools in the town centre were also shut.
A council spokeswoman said while water levels were dropping, further rainfall is expected locally through the night sparking fears of more flooding.
Around 30 army personnel with four vehicles were assisting local authorities in the area.