FILE - Smoke rises after an attack by Houthi rebels on the city of Taiz, Yemen, on Oct. 21, 2015. (AP Photo/Abdulnasser Alseddik, File) Abdulnasser Alseddik/AP hide caption

Abdulnasser Alseddik/AP

Drinking water has been scarce for over a decade in Taiz, but the problem has reached crisis levels in recent weeks as Iran-backed Houthi rebels besiege Yemen's third-largest city in their escalating conflict with government forces.

The needs of Taiz's more than 1 million residents are now barely being met, humanitarian groups say, as access to wells is limited, desalination plants run low on fuel and water delivery trucks are largely prevented from entering the city.

Families are rationing every drop.…