To answer the OP question, yes, there must be hundreds, if not thousands of home brew watermakers out there. It is not Black Magic, its just physics.
These probably even include a few evaporative units, which still need some sort of pump to create vacuum and remove product water
Watermakers on boats probably form the minority of plants installed. A lot of municipalities use this method.
There is no need to be held hostage by the "marine" world and boat shops, try looking at jurby.com to see what I mean. You can buy a 60lt/h membrane there for about 180 Euros. (Some of the "marine" manufacturers source theirs there)
I have a design for an evap unit. Actually when I was at sea professionally that is all we had.
The biggest advance in water
treatment or water makers is going to be the advent of Graphene. This material promises to be able to make potable water out of sea water at pressures of less than one Bs. (14.7 Psi)
Imagine a watertank under the waterline in your bilge
, with a seacock to the outside, and a spiral wound drum filter of Graphene keeping your tank full of drinking water
powered by the pressure of the sea water outside the hull