Residents and visitors to one of the three Aran islands have been advised not to drink water from its private water scheme after more than 50 people were taken ill in recent weeks.
The local co-operative on Inish Maan, which operates the group scheme, has advised people not to drink the water until they are given the all-clear.
Tests carried out last week showed high levels of E. coli in the water. The Western Health Board has also carried out tests on the water and deemed it unsuitable for consumption.
The island has a population of about 200 people, who between them use some 20,000 gallons of water each day. A large number of visitors in recent weeks has resulted in a doubling of the daily water consumption.
A number of the scuba divers using the island's popular dive centre reported signs of illness and a 14-year-old visitor had to be airlifted to the mainland for treatment.
During the past fortnight, the island's hotel, pub and bed-and-breakfasts have stopped serving local drinking water, although no signs have been erected in prominent places to warn visitors of the dangers.
"We have distributed 1,600 five-litre containers of Galway water to householders to tide them over," said the manager of the island's co-op, Mr Pól Ó Foighil. "We accept that our water supply was polluted, but 41 per cent of the country's group schemes are polluted."
The problem first arose when water levels ran low earlier this month.
Mr Ó Foighil said that the co-op was using chlorine to clear the E. coli from the island's reservoirs.