Timing
It all depends on how fast things happen. If it's quickly they'll just die. If it happens over and extended time their will be mass migrations of non-sustainable populations world wide to areas with more resources. Translated, that means they're coming for the water - and the food that you think of as "yours." The future is described by a thirst and a hunger that this planet has never known - unless we get back to sustainable population levels before we reach catastrophic tipping points - if we haven't already.