The city of Atlanta has a bit of a problem. It gets all its water from one reservoir, one that is also legally obligated to feed a river where an endangered mollusk lives. Not only that, but it is also not allowed to deprive Florida water from downstream.
Atlanta has been growing significantly for the past few years. New developments spring up every day, and everyone wants to drink water, shower, grow a lawn, and wash their dishes and clothes. They will lose this ability if the reservoir dries up, and unfortunately both the east and west coasts of the United States are undergoing a severe drought. Atlanta had 90 days of water left....60 days ago.
Water does not appear by magic. It must come from somewhere, either rain or importation. The Los Angeles region, where I was born, imports water from northern California, which has enough for both regions. Unfortunately, the regions around Atlanta don't have spare water, so this option is out.
Water can be reprocessed, removing the pee, poop, soap, and various chemicals that go into waste water, and then filtered through the earth. This produces clean water, the natural way. If you think it's gross, I guarantee you that any given glass of water you pour, be it from a tap or a bottle, has been through at least 12 different animals in the past. But let's assume that this strategy also is rejected for the ick factor, like it is in Australia.
However, Atlanta is reasonably close to the ocean. I therefore propose that a desalinization plant be built between the two. The plant would force filtered seawater at high pressure through pipes made of a membrane. The reverse osmosis reaction would cause fresh water to leak through the membrane, and concentrate the water still in the pipe as brine. The brine could then be evaporated into sea salt, and sold at a premium. The fresh water would be piped into the reservoir.
This plant would be very harsh on the power grid, (because pumping at high pressure uses a lot of electricity), and so I also think the plant should have a power generation plant built next to it. I recommend nuclear, as it is inexpensive to run and will not pollute the air. However, since people tend to have hysterical reactions to nuclear power, coal will probably be substituted. Coal would work almost as well, if one doesn't mind the bad smelling smoke.
I estimate, very roughly, that the nuclear plant would cost about $9 billion, the water treatment another $1 billion, and $1 billion to lay out the pipes between the ocean, the plant, and the lake. For $11 billion dollars, Atlanta has fresh drinking water for the rest of American existence.