Irish Water says it cannot give an estimate on when the boil water notice will be lifted for over 17,000 customers in County Longford.
The measure was taken last night as a precautionary measure over concerns that a small amount of cryptosporidium may be present in the supply from the Central Public Water Supply.
Areas affected by the notice include Longford Town, Newtown Forbes, Ballinalee, part of Edgeworthstown, part of Drumlish, part of Killashee and surrounding areas.
John Gavin Operations Lead with Irish Water says that deterioration of water quality from the Lough Forbes source has prompted the action:
"The raw water quality in the lake has deteriorated somewhat. This may be a seasonal thing that can happen in lakes, and it has come through the treatment processes and we found that a number of the filters that the water was cloudier than would be our normal high standards for each of the filters.
We imposed a boil water notice on the basis that we were concerned that a small amount of cryptosporidium may have got through the treatment processes."
Mr Gavin says they are unable to give any certainty to customers as to when the supply will be fully safe for the notice to be lifted:
"We are currently working in order to get the boil water notice lifted. The HSE and ourselves have to agree what results will allow us to lift it.
In the meantime, it is somewhat out of our full control in so far as the raw water quality will have to settle somewhat. Once we have it settled we will be running the plant as normal and when we get a series of results that satisfy the HSE we will lift the boil water notice.
Unfortunately, at this stage, we can't say when that could happen."
You can hear the full interview with John here: