Lack of fresh water in the US is a solvable issue. We have oceans all around us and the US has the know-how to ship fresh, desalinated water from the coast to middle america.
BTW, this issue is solvable if everyone agree that meat should be rationned: no corn and some GMO wheat to produce carbs for human consumption only, a lot more vegetables and more forestry could do the trick.
That's ~724MM/day in water costs or 264B/year for water. US GDP is 21 Trillion.
As cost of water increases, conservation becomes more economical. Say all agriculture switches to hydroponics as a result. Hydroponics uses 1/10th the water of traditional methods...so we're talking now just 26B/year of water costs.
In 2017 US farms spent 359B on operations.
Food will become more expensive, but overall we'll be fine.