The United Nations humanitarian coordinator in Iraq has said drinking-water conditions in the frontline city of Mosul are now "catastrophic."
Lise Grande's comments on November 30 come as Iraqi government forces, backed by Shi'ite militias, Kurdish fighters, and U.S. air power, continue their advance within the city.
The city has been under the control of Islamic State (IS) fighters since 2014.
Retaking the city would be a major victory for Iraq's fragile government and a major blow to roll back IS's territorial gains.
"Nearly half a million civilians, already struggling to feed themselves day to day, are now without access to clean drinking water," Grande was quoted by AFP as saying.
"The impact on children, women, and families will be catastrophic," she said.
Since the offensive began on October 17, more than 70,000 people have fled the fighting.
More than a million others, however, are believed to remain in the city.