A new solar desalination system takes in saltwater and heats it with natural sunlight. The system flushes out accumulated salt, so replacement parts aren’t needed often, meaning the system could potentially produce drinking water that is cheaper than tap water.
A claim like that sorta sounds suspect.
Depending on how one gets their tapwater, it could be as simple as drilling a hole in the ground and getting the water, or putting a bunch of sand in a basin. The per liter cost of getting intermediate raw water from a slow sand filter is infinitesimal, pennies per cubic meter. Water from a slow sand filter must then be chlorinated for distribution, but so does water from a desalination plant because chlorination isn’t just for treating the water coming out of the tap, but it’s for protecting the water as it goes through water lines.