It is estimated that more rain fell in an hour on Tuesday evening than in the entire previous month in Co Wexford, a county council spokesperson said.
Businesses trying to recover from losses incurred by Covid-19 were dealt a further blow after they suffered flood damage as a result of the "biblical-like" downpours caused by thunderstorms.
Met Éireann says more heavy rain is expected and a weather warning is in place until 3am on Friday, with more flash flooding predicted.
The Holy Grail restaurant, which had been running a takeaway service in Enniscorthy town, had to temporarily close and will now need to install new floors.
Diane Rigley, manager of the restaurant, said the water came gushing in and could not be stopped.
"Luckily the fire brigade came along and were able to clear it but there was a lot of damage done to the floors," she said.
Wickham Bros butchers also suffered water damage on its shop floor and basement but is remaining open.
Owner Mark Wickham said: "We can't afford to close after everything that's happened lately.
"We've some competitors in the town and after being closed due to coronavirus we've had to stay open. It's the last thing you'd need after the last few months."
A spokesperson for Wexford County Council described the flooding as of "biblical proportions".
"The level of rainfall experienced in Enniscorthy town was unprecedented in its force. It is estimated that more rain fell in an hour than in the entire proceeding month."
Meanwhile, a yellow rainfall warning is in place for Leinster as well as counties Cavan, Monaghan, Donegal, Leitrim, Roscommon, Sligo, Tipperary and Waterford until 3am tomorrow.
Met Éireann's Liz Walsh said more thundery downpours are expected. "There is greater risk of prolonged periods of rain later today and into the early hours of Friday," she said.
"With thunderstorms it's very hard to pinpoint exactly where they will happen but we do realise that some people will not see anything at all when 4km down the road they will see a torrential downpour.
"Heavy rain is possible on Saturday mostly everywhere."