Motorists have again been urged to exercise caution on the roads following overnight frost.
Gardaí and the PSNI warned drivers that frost and black ice are making driving conditions difficult.
AA Roadwatch said roads are particularly hazardous in parts of Munster, south Connacht and the Midlands.
Met Éireann said frost and ice will clear slowly today and the day will be mainly dry with sunny spells and highest temperatures of 4 to 8 degrees.
In Northern Ireland, icy conditions persist following overnight sub-zero temperatures.
Water restrictions are to remain in place in Dublin this weekend, but storage levels in the capital's reservoirs are improving.
Dublin City Council said it will review water supplies tomorrow and may begin to lift restrictions. It said a full picture of the supply situation will not be apparent until the middle of next week once schools and colleges have returned from the Christmas break.
Night-time water restrictions were lifted entirely earlier this week in Cork city, Kerry, Limerick city and county, Leitrim, Mayo and Donegal.
However, thousands of residents on the east side of Galway have no water this weekend, or have a disrupted supply. Galway City Council says it is attempting to increase reservoir levels by restricting supply between 10pm and 7am.
Galway County Council said some farms south of Ballinasloe are affected due to leaks in the Kiltormer and Laurencetown areas.
The Northern Ireland Met Office reported that December was the coldest month on record. A new low of -18.7 degrees was recorded by the Met Office station in Castlederg, Co Tyrone, where the record was broken twice in the four days just before Christmas.
The same station recorded a continuous sub-zero spell of 211 hours lasting from December 17th until St Stephen's Day.