Is the water in the rivers and dam going to be clean water or it have radiation and all dirty?
The Colorado drains a large area of the United States, going through Most of Colorado, part of Utah and all of Arizona. So, if those watersheds were irradiated from fallout from nuclear blasts, then the water in the reservoir will be irradiated. We know that the Vegas area was spared from bombs, so the radiation in the water may not be as high as around DC. Or, if it has accumulated over time, then it could be as bad or worse than DC.
So, it could be either way in this game.