Almost all the Salt
water (SW) type Reverse Osmosis
(RO) filters require upward of 500 Pounds per Square inch of pressure. There is no DC motor
, of a reasonable size, that will generate sufficient pressure for salt water RO by themselves. There are AC pumps that can do it. There are mechanical pumps which can readily do it. All the other DC solutions use a form hydraulic intensifier to get sufficient pressure (flow requirements are there too). So, most likely, that's not a SW unit, or a significant piece is missing.
Couple of additional points. Desalination makes a lot of sense when you're moving, cruising. It makes far less sense when you're sitting at a dock
and water is available from a hose nearby, even if you have to do extensions! Second, it may not be the water that is insufficient for 30 gallon showers, it may be the available hot water. 12 gallons of hot water is rather large for most mid size boats. 8 gallons is fairly normal and even 6 gallon units are very common. After you use about half the tank, you start to find that you need a much higher % of hot water to cold. This means you have even less water available for the shower
. So, in most cases a 10-16 gallon hot shower
is going to be at or around the max. When my wife washes her hair, that's about what she uses.