The water is there, but you cant drink it straight from the source. There is an inherent cost to that. The Israelies have gotten the cost down considerably. I think they can make a cubic metre of water drinkable for about $48. Graphene, because it is very cheap, will make it even cheaper. It can bring the cost down into the $30’s.
There’s still the cost of pumping and distribution. But still, if the cost is bearable, imagine the interior of Australia becoming a breadbasket rather than a desert. Or the Sahara blooming.
Israel can make 1,000 liters of seawater into drinking water for $0.58. http://www.nextbigfuture.com/2016/07/israel-has-desalination-fresh-water.html?m=1