HRO Systems Seafari Water maker

While the term "water maker" might conjure up visions of natives dancing and chanting imprecations around a campfire at night or a wild-haired man in pointy hat and cloak grinding unidentifiable powders in a mortar, a modern water maker is not quite as arcane but performs a function that is almost as miraculous as turning base metals into gold; it converts salt or brackish water into clean drinking water that is close to the purity found in distilled water.

The basic principles used in reverse osmosis are understandable - take water, run it through one or more normal filters to get rid of big particulates and then pump it, under extremely high pressure, through a very fine man-made filter. What happens under the covers is a bit more complex than mere high-pressure filtering.

The Horizon HRO system that I have is incredibly power hungry, consuming the complete output of my generator when running, if I run other consumers the generator cooling water starts turning dark with carbon, a sign of overloading. While the device does need a lot of power it produces quite a bit of water. One can adjust back pressure manually and I turn the water maker down from maximum and make 1 liter per minute - making it easy to calculate how much water I am returning to the tanks. In total I have 750l of water but in practice I will use only one of the tanks (~240l) and run the generator 4 hours to fill it up again; at the same time I'll top up the batteries so that they get to "float". One needs to adjust the back pressure on the water maker each time it runs, that pressure and the amount of clean water produced is dependant upon the ambient temperature, the salinity of the water, the amount of pressure and back pressure and the general cleanliness of the filters and system. It makes little sense to run the water maker for just a short period, since once the generation process is complete it performs a clean cycle, which uses about 10l of water - so you'd barely break even if you ran it for 11 minutes.

Unfortunately the special pressure filtration unit used in water makers is very sensitive to pollutants, particularly to fuel, so the one time when one has a lot of spare power, when hooked up to the power grid at dock, is the one time when one can't turn the darned thing on. On the other hand, when at dock it is easier and most likely cheaper to fill up with water. This works well where the water supply is clean, but I prefer to make my own water and thus know exactly what it is that I've put into my tanks.