Intensified bombings on the Syrian city of Aleppo have left at least two million persons without water, the UN said.
UNICEF said fierce strikes on Friday prevented repairs to a damaged pumping station supplying rebel-held districts of the city, BBC reported.
A station pumping water to Aleppo had been switched off.
Fresh strikes were reported in the city on Saturday, as the Syrian army pressed on with its push to retake rebel areas.
The Syrian Observatory for Human Rights, a Britain-based group monitoring the conflict, said at least 25 persons, including women and children, were killed in fresh air strikes on Saturday.
Unicef Deputy Director Justin Forsyth said: "Aleppo is slowly dying, and the world is watching, and the water is being cut off and bombed – it is just the latest act of inhumanity."
A Unicef official said that the lack of running water could be "catastrophic" as residents now had to resort to contaminated water and were at risk from waterborne diseases.
He said water was being used as a weapon of war by all sides. The pumping station supplying rebel-held parts of Aleppo was damaged on Thursday and subsequent strikes had made repairs impossible, the official added.
"That pumping station pumps water to the entire population of the eastern part of city – that’s at least 2,00,000 people and then in retaliation for that attack a nearby pumping station that pumps water to the entire western part of the city – upwards to 1.5 million people – was deliberately switched off," the official told the BBC.
Activists said both Syrian and Russian warplanes were taking part in the latest offensive, though Russia has not confirmed its involvement.
Russia supports the Syrian government, while the US backs the opposition. The two powers accuse each other of failing to rein in their respective allies on the ground.
Medical sources said at least 91 persons were killed in Friday’s bombardment.
The Syrian army has said that it is preparing for a ground offensive, and told civilians to stay away from rebel positions.
On Saturday government troops were reported to have captured the rebel stronghold of Handarat to the north of Aleppo, further tightening their grip on the city.