Dehydrate in a building with running water. Is drinking from a tap a lost skill?
Why not shut off all water and power to the bldg? Let them wallow in their own sh#t, and have no drinking water or sewage service. Also, no way to charge their “handheld devices”. Absolutely no food permitted in. Form a perimeter around the bldg and let no one near it until they all come out. It would all be over quickly, safely, and inexpensively.