'Extremely high water stress' afflicts 83% of the population in the Middle East and North Africa and 74% in South Asia.
The border crossing is essential for more than 4 million uprooted people in Syria who depend on humanitarian aid.
Syrian President Bashar Assad, formerly ostracized by most Arab nations, was warmly readmitted to the Arab League.
"The tragic reality is that an effective response was hampered in part by challenges that relate directly to the unresolved issues at the heart of the conflict," the U.N. special envoy to Syria, Geir Pedersen, told the U.N. Security Council.
Disasters and conflicts drove nations atop a list of places adding to the 28 million people newly displaced at home.
The kidnappings of the three ICRC staff six years ago had been kept secret until now out of fears for their safety.