I've always figured that we don't use desalination as much on land because we seem to be much less willing to combine operations on land than we do on Navy vessels, besides just the cost compared to other land based water gathering methods. For instance, as a mechanic/engineer onboard the ship, I helped make the steam, electricity and water for the ship all in basically the same space or working with people in the space next to ours to do this. We used all of these things together to make the others. For civilians to do this and be as efficient as possible, they would basically have to integrate the desalination plants into close operation with an electric power plant near a large body of water, preferably the ocean. Plus there is the issue of more pollution being in the water closer to land than at sea. That means ensuring better monitoring of water than we do (we don't generally have to worry about foreign chemicals in our water, just microbes, bacteria, and maybe some algae, by the time we make the water, the chemicals have already diluted to pretty much undetectable levels). And then there is the matter of what to do with the "brine" (concentrated salt water left over with other sealife/crud within it that we simply pump back out to sea) that is left. We simply pump it back out to sea as we pass, whereas piping would be needed to this on land but it might need to be processed to meet pollution standards.
It's certainly possible to do that right now, I just think most people feel it isn't worth it when there are other sources available that are cheaper to do. One day we might need it though, considering how much water we use, and hopefully we will be prepared for it without major hassles, but I doubt it.
