Great, now that people are supplied for a couple days let's get into the meat of it. People with wells can supply their neighbors and sell excess water for a nice profit, the police and fire department can take over the reservoirs and help with transport and filling containers...

Okay considering the downvotes I suppose I should have laid out my point at first: We use far far more water than we actually need. In an emergency situation it's not extremely hard to get a couple of gallons a day to people.

Unless by water supply we actually mean turn off the rain. I have no response to that one. That's not going to impact society, that's going to kill almost every bit of land life across the entire earth.