1.8 million people in Aleppo without safe drinking water
A technical failure in Al Khafse water station near Islamic State-held al-Bab has meant 1.8 million civilians in war-ravaged Aleppo have been cut off since 14 January.
The three pumping stations in Aleppo city - Sulaiman Alhalabi, Bab Alnerab and Tishreen - are also not functioning.
The UN said it is supporting the response to the water crisis.
"Though the issue at hand can be technically fixed, ISIL is not allowing repair teams to access the water station for repair works," the UN said in a situation update on Saturday, using an alternative acronym for the militant group.
In the interim, the Aleppo water authority is operating 90 wells that are providing access to water for almost one million people.
The UN has installed 61 tanks and rehabilitated an additional 100 wells throughout the city while UNICEF continues its water trucking activities at the rate of 6 million litres per day to 400,000 people, in addition to supplying fuel for the operation of wells, and water purification materials.
The International Committee of the Red Cross and the Syrian Arab Red Crescent are among humanitarian agencies installing water tanks, repairing wells and providing additional water trucking services.
UN agencies were able to reach the devastated city to deliver life-saving aid in December, after the Syrian regime retook Aleppo in a devasting Russian-backed offensive.
The security situation in Aleppo city has remained comparatively calm, the UN's office for humanitarian affairs (UNOCHA) reported, with only sporadic mortar incidents reported.
In east Aleppo, the neighbourhoods of Hanano, Tariq al-Bab and al-Qaser continue to host the largest numbers of returnees, with respectively 16,500, 14,194 and 10,260 people, UNOCHA said.
However, to date, no structural assessment for damaged buildings has been carried out even though many of the buildings are structurally unsound and pose a severe threat to residents.
The UN on Friday approved $19 million in aid from the Syria Humanitarian Fund to provide immediate assistance.