Energy costs are the major limiter to desalination and the availability of water more broadly. One or two people can do that but if an entire civilization does it they'll clearcut their forests and make the air unbreatheable. Cooking fires are a major source of air pollution in many Indian cities.
I think these systems were always intended for small scale use for detached villages and whatnot? I don't see a way they would be able to provide for city even if you made hundreds of thousands.
If you want to support a civilization you better switch to something that can exploit the volume for increased efficiency, like an actual desalinization plant and a solar concentrator powerplant to run it.