I know it doesn't vanish, but it can be relocated -- there's no promise that water taken from one area will be released in such a way that it rejoins the natural flow -- it could easily be locked up in some form, whether that be sewage or storage, or simply bottled and sent elsewhere. Depending on the water's use by whatever desert society is using it, it may never be released back into the system. Unlikely to have a major effect, I know, but I don't think anybody makes the argument that dams don't have an impact on how water flows in an environment. To me, that's what this is. A wind dam. Small now, but...