Roscommon County Council officials have launched an investigation into how hundreds of gallons of diesel contaminated a local lake yesterday, causing them to shut off water to over 5,000 homes.
Tankers of drinking water have been placed in the towns of Strokestown, Elphin and Tarmonbarry. The council says cutting off the water supply could last for the rest of the week.
Householders have been told to collect rainwater to use in toilets as the council moves to flush the diesel from Lisheen Lake, the only source of drinking water in the region.
"One of our employees noticed the diesel in the lake this morning, and we immediately took steps to investigate it.
"It had entered the system as far as an intermediate reservoir at Kiltrustan, but had not got as far as the main reservoir at Strokestown," said council spokesman Ciarán Madden, who declined to comment on the source of the diesel.
"The diesel came into the lake from a stream, and we have put booms across that stream. We hope we have stopped the leakage, but we can't be sure yet.
"If you go down-wind of the lake you can smell the diesel 20m away.
"We have to stop the entire water supply to clean out the system.
"So people have no water in their toilets, and we would ask them to collect rainwater to use in their cisterns.
"There is plenty of water out there, but we can't pump anything through the system until we get the diesel out of the water. It could take a few days.
"At this stage we don't know how long it will take us," Mr Madden said.
The water shortage has hit the towns of Strokestown, Elphin, Rooskey, Tulsk and Tarmonbarry.
Local Fianna Fáil councillor Eugene Murphy said as many as 10,000 people could be affected.
"It is causing great disruption to private residences, businesses, schools, and other institutions.
"I would appeal to locals to co-operate with the instructions of the council officials which are posted on their website and in the local media," said Mr Murphy.
Lisheen Lake is not believed to have any significant amount of fish life, and Mr Madden said there was "no evidence of a fish kill".
The council called in experts on water contamination to help them in their efforts yesterday.
Gardaí in Boyle said they had not received any complaint about the contamination.