Water is a finite resource. The amount of water on Earth is constant. It can be moisture in the atmosphere, ice in the artic, fresh water in an aquifer, ocean, lake,river, stream etc.
As the world population grows over the rest of this century there may not be enough fresh, potable water for everyone on the planet.
I'm not a scientist but I would suspect that the areas of our country that are drier would be hit first.
By desalinizing the salt water in large quantities this could ease the burden somewhat and provide a continuing source of fresh water for our country.