A Dehumidifier connected to a water filter?
It sounds like there is more to it, based on their comment about using as little energy as possible. I would love to have a solar powered one that could be used to water livestock. I live in KY, which gets really humid. It would be a gusher.
I expect a filter & UV purifier would be necessary, given this thing exposes concentrated moisture to airborne contaminants indefinitely. That and our American paranoia for absolute purity in consumables.