from ishipaco's site : Katadyn and PUR Watermakers: Installation, Maintenance and Troubleshooting
Can I use my watermaker in freshwater? The short answer is—yes. There's nothing about this subject in the Katadyn
Owner's Manual, but I've had verbal confirmation from the Katadyn
engineers in Switzerland: processing freshwater will not damage a Katadyn watermaker.
At the present time, I am not aware of any competing brand of watermaker whose manufacturer recommends using their watermakers in freshwater; and the common wisdom among owners of those brands is that freshwater input is not allowed. I suspect that this may be because most other brands of watermakers have pressure regulators which the user can adjust. Watermaker membranes can be damaged by internal pressures that are too high and, because of the complex physics of reverse osmosis
, the chances of overpressurizing the membrane are greater when processing freshwater. It is possible for a user of other brands of watermaker to accidentally damage the membrane by adjusting the working pressures, even when using a setting that would be perfectly O.K. when processing seawater. Because of this, the rumor among cruisers is that watermakers should not be used to process freshwater. It may be that Katadyn watermakers, with their system of automatic internal pressure regulation, are the only exception to this general belief. As far as I know that is, indeed, the case.
I became interested in this subject after reaching the Caribbean
side of the Americas and while spending a hurricane
season at Mario's Marina in Rio Dulce, Guatemala
. The marina is about twenty miles up the river, far from the ocean. I've never taken on dockwater while cruising foreign waters and didn't want to start there. So I ran my watermakers (a PUR Model 35 and a Katadyn Model 40E) while tied up to the dock
for almost six months. A couple of years prior to that, I had run my watermakers in the estuary at Bahía de Carácas, Ecuador
, for six months. The water there is a dirty mix of fresh river water and seawater.
Although Katadyn watermakers will work well with freshwater input, I have a word of warning. Most freshwater situations should be considered "enclosed water spaces." In such locations, especially in third world countries, rivers are often used—legally or otherwise—as sewage systems. The more populated areas there are upstream from your location, the more likely you will be exposed to various kinds of contaminants—everything from human waste to petroleum products to pesticide runoff. Your chances of experiencing problems from such sources are significantly greater than when in the open ocean. Keep this in mind.
In my own case, to be honest, I had to replace my membranes after six months making water in the Rio Dulce. The membrane elements became slimy and over time the TDS readings rose gradually to the 6-700 ppm range. Bottom line: the problem isn't freshwater, per se, but what other things are likely to be found in the freshwater.