Hi
Is there any way to force WEAP to fully supply some demands like city?

Dear Amir,
You can set the Demand Priority for your city to "1" and the Demand Priority for all other demand sites to "2" or greater. You can do this when creating a demand site, or later by right-clicking on the demand site, choosing "General Info" and then changing the Demand Priority.
Of course, if there is not enough water in your system (or the water transmission is volumne-limited), your city will not always have its demand fully met.
You can find additional details in the Refining Demand Analysis section of the WEAP Tutorial.

Anne