Boil water notices are in operation in three counties due to industrial action at several water plants, Uisce Éireann has said.
Head of Asset Operations Tom Cuddy said there are pickets at 17 water treatment plants.
Boil water notices have been put in place for a number of areas in Waterford, Tipperary and Cork, impacting around 100,000 people.
Speaking on RTÉ's Morning Ireland, Mr Cuddy said: "At seven of those plants we have boil water notices in place because of the risk and those are in counties Waterford, Tipperary and Cork.
"We are continuing with supply but because of the risk and the prospect of water quality deteriorating we have boil water notices in place."
The ongoing dispute is between the Unite trade union and local authorities.
Mr Cuddy appealed to workers to cease the industrial action saying it is having a significant impact on people and said the action is "excessive" and "disproportionate" to the issues at hand.
He said that with a plant "not being manned for three days, while we can set up everything in a certain way that is stable, the weather can change and circumstances can change and so we cannot take the chance on that."
He also responded to the demands by Unite who want to be assured that staff transferring from local authority employment to Uisce Éireann will retain their public service status.
Mr Cuddy said a framework has been put in place by the Government that gives extensive guarantees on terms and conditions and assurances for all workers.
He said all the other unions and other worker representative groups have come on board for the implementation of that and they would encourage "these people to go along with their colleagues and to engage in the same manner."
He said Uisce Éireann has has already embarked on working with the Irish Water consultative group in order to "tease out the details".
Unite has said the industrial action is due to the "continued refusal of local authorities and its representative body, the Local Government Management Agency (LGMA) to meaningfully engage with the union over its members' concerns regarding shortcomings to the 'Framework for the Future Delivery of Water Services’ document put forward by the Workplace Relations Commission last year."
Uisce Eireann said the boil water notices may remain in place for several days after the industrial action ends to ensure water is safe to drink.
The areas under boil water notices are:
Cork - Glashaboy Public Water Supply, Townlands, Glashaboy
Waterford - East Waterford Water Supply Scheme, Ballylaneen Water Treatment Plant, Stradbally Water Treament Plan
Tipperary - Carrick an Suir (Crotty Lake) Public Water Supply Scheme, Glenary Public Water Supply, Clonmel Poulavanogue Public Water Supply
