Director of Services Kieran Hayes told a council meeting tonight that the contamination is the worst ever recorded in Ireland.
Mr Hayes said it will take until September to bring water from other treatment plants but, in the short term, putting filtered water fonts at different points around the city is being considered.
Meanwhile water supplies were being disrupted again today in parts of north Co Dublin, with traffic diversions put in place to allow for emergency repairs.
The areas affected include Malahide, Kinsealy, Feltrim and Swords.
A replacement pipe also burst and is causing the current problems.
Water tankers are in place at The Grand Hotel, Malahide, Kinsealy Shopping Centre carpark and Dunnes Stores, Portmarnock.
Traffic diversions were in place on Forrest Road and Main Street in Swords to allow emergency work to be done.
Motorists are being asked to avoid both locations.
Fingal County Council says it is hoping to have the water service restored by tomorrow morning.
