An important thing to remember about the AC vs DC water maker question is that the only difference is how do you get sea water up to 800psi to drive a portion of it through the RO Membrane. I know that seems basic and almost obvious to say, but starting with that understanding can help with the decision. Sure different brands of water makers have varying levels of automation, control and features but at the end of the day that fact drives Cost, Fresh Water Production Rate, Power Usage, Maintenance
The focus of the DC approach is energy efficiency and giving the client the ability to run the system from their battery
bank, so good DC systems use an energy recovery pump to get sea water up to 800PSI. But this focus on low energy usage also makes you will live with low production and need to run the unit for longer periods. The energy recovery pumps also add in cost, so expect to pay more for a lower output DC system.
The focus of the AC approach is High fresh water production, the AC approach says we have power available while running the generator, so lets make as much water as possible and use a energy hog off the shelf piston pump. This approach can give you a 30GPH water maker for almost 1/3 the cost of a 20GPH DC energy recovery system, so if the goal is having larger amounts of fresh water and you have a generator available then the AC system usually wins out. But if the goal is running off solar and your batteries, then you have to go with a lower output DC unit.
A common worry going the AC approach is what if my generator goes down...do I then lose my ability to make water? No, not if you have a 2000W inverter
, you can make water through your inverter
. Our approach is to use our generator to make water while at anchor
and then when underway with the alternator
running, once the batteries become topped up, we turn on the water maker through the inverter being powered by the alternator
. So that way you have a back-up approach for if something happens to your generator. Now unless you have LiFePO4
batteries, it is unrealistic to think that you will run a high output AC water maker off of your battery
bank using just wind
and solar...but it can easily be done while running your alternator.
There is no "wrong answer" in the AC/DC decision, as long as you know the pluses and minuses to each approach and line that up with your cruising plans and expectations. Speaking in generalizations (which is always risky) the owner and crew of a 42ft Cat tends to have different expectations than a smaller mono hull
cruiser in terms of comfort, showers, deck
rinse-downs, and general water use. It is much easier to meet those expectations with a higher output AC water maker than a lower output DC system.
Here is a link to download a copy of our SM30 (33GPH water maker for $5250)
Of course I am a predisposed to like the AC approach not just because I build and sell them, but because our family
of 4 would not be on year 9 of cruising and living aboard
if I had to tell my wife and daughter to constantly be watching their water use. Part of meeting our expectations for comfortable cruising and living aboard
was having unlimited showers and a washing
machine, so the AC high output water maker was the best way to meet our expectations.