Why Didn't They Drink Soda? Juice?

I thought the idea for this movie was a good one, but it was somewhat spoiled by a fatal plot flaw. Not being able to use tap water for anything would be terrible, but the biggest impact, at least at first, would be the inability to wash. (Since the authorities did not actually cut off the water supply, at least you could still flush the toilet.) There are plenty of other beverages in most homes and in stores to last a few days at least. No doubt there would be panic and hoarding, but implying that people are dying of thirst within 3 days is pretty silly, even in LA in the summer.