Watermaker Maintenance… and Repair

Miss Miranda is equipped with a watermaker, which we found to be a “nice to have” up in the Pacific Northwest, but is a must have down here in Mexico. Our boat holds a little bit less than 300 gallons of water, and we tend to use 20-25 gallons a day, depending on how often we shower and do laundry. So we have at most a 10 day supply on board. Given the general scarcity of water in Mexico, where it is common that people have water delivered to their homes, it is important to be able to make our own. Anyway, when we left the boat in March of last year we “pickled” the watermaker for long term storage, which consists of adding a chemical preservative to the system… kind of like winterizing the domestic water system on a boat or RV.

We just got around to “unpickling” the watermaker in yesterday, in part because we were waiting for a new filter, as one of those we sent down with Red Rover was the wrong size. The unpickling process is pretty straightforward. It involves allowing the system to fill with fresh water to displace the preservative and then circulating fresh water for a half hour or so. Next, we put in new filters, and then we were ready to test the system by making some water. Everything seemed to work perfectly… except the “product” water was contaminated with a chemical taste. We have a TDS (total dissolved solids) tester that allows us to check the quality of the water, and it was reading well over 950 PPM, even after making about 15 gallons of water. As a reference, the TDS in our filtered drinking and tap water on the boat is 150-160 PPM, and any water over 500 PPM is not considered safe to drink. Seawater is about 35,000 PPM!

It was now time for some professional help, so we called Hector Marine, who is the local watermaker dealer. He had two techs over on the boat within an hour, and they found the same thing – the watermaker was working properly (meaning it was producing fresh water from salt water) but the quality was poor. They saw PPM readings as high as 4000, and not lower than 1500. From this they concluded that the membrane needed to be replaced. This was not terribly surprising, since it was last replaced by the previous owner in early 2015, and the average lifespan is about 5 years.

The membrane is the real guts of the watermaker, and it works via reverse osmosis. Put simply, salt water is pushed through the membrane at high pressure. The membrane prevents salt from passing, so what comes out is fresh water. About 10% of the water pumped into the membrane assembly comes out as fresh or “product” water, and the remaining “brine” is pumped overboard. Our watermaker can produce about 30 gallons an hour or a little more than a day’s usage.

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It turns out that they have the membrane in stock here in La Paz, so they removed the assembly and took it to the shop to install a new membrane. The very next afternoon they were back to reinstall the assembly on the boat.

After about 30 minutes of installation and flushing with fresh water, we were ready to test the watermaker. After just a few minutes of run time, it was producing product water at 238 PPM, which is just fine.

I am super impressed with the quality and speed of the work done by Hector Marine. It is almost shocking to have a job like this, especially one that requires a replacement part, to be completed in just about 24 hours!