Some of the best currently operating desalination plants have total costs of 0.044 cents to 0.4 cents per gallon per day. Most costs are about 0.1 to 0.2 cents per gallon per day The costs are often dependent upon the cost of energy. Waste water reclamation costs usually costs about 0.15 cents per gallon and ground water 0.1 cents per gallon. Desalination is about a $5 billion per year business.
There are those looking at applying nanotechnology to supply fresh water such as the organization Nanowater. There was a Wired magazine article on this in 2004 Here is CBC article on Canada, Russia, Brazil and China having most of the world's fresh water