Watermaker maintenance


At this point, I’ll assume you have already installed your watermaker (or at least read the article on Installation on this website) and are interested in how to use it correctly. It’s really not hard, as long as you’re aware of a few “gotchas” that can make your experience frustrating. To avoid the most common stumbling blocks, all you have to do is continue to read on (and, of course, pay attention.)

Like most equipment on a cruising vessel, the watermaker likes to be used. From my experience, one of the best ways to increase the chances that something won’t work the next time you need it is to let it sit idle for a long time. Good maintenance habits can go a long way toward reducing these kinds of problems. A good example: when your boat’s engine isn’t going to be run for a few months, you should change the oil at the beginning of the idle period and not wait until just before you need to use it again. That good habit avoids leaving the engine lower end components (e.g., crank, rods, bearings, seals) sitting in the old oil, exposed to the acids and other crud that have accumulated from its prior use. You do that oil change, don’t you? O.K., you don’t have to answer. How about an example closer to home—have you ever parked the boat for an extended period and neglected to pull your knotmeter transducer and replace it with the plug? ‘Nuff said.

Hopefully, you gave some thought about your expected potable water needs before you actually went out and purchased a watermaker. The Katadyn 40E is a great choice for cruising vessels requiring up to 10-15 gallons of water each day. The “40” in the model name indicates the nominal number of gallons it is capable of producing in a 24-hour period. Of course, you shouldn’t be needing to run your watermaker 24 hours a day to meet your needs. If that’s the case, you should definitely consider upgrading to a larger capacity unit, like the Model 80E or 160E, or even one of the “big boys.”

I’ll use my own situation as an example. We typically use an average of about 5 gals./day. There are two of us on the boat and we’re not terribly conservative about our water consumption. We even do the dishes using potable water. To meet that level of consumption, we run our watermaker on average about four hours a day. In reality, we usually run it for a longer period every second or third day. We’re also careful to make more water well before we’re low on our available supply. As I mentioned in the article on Installation, we arrange our watermaking schedule to assure we always have at least 12 gallons of potable water at all times, either in our main storage tank or in our jerry jugs. This is a habit we developed for our frequent bluewater passages. It’s a precaution to avoid being caught without enough potable water to survive an equipment failure during a long offshore voyage.

I consider our schedule close to perfect, based on over a decade of experience using the watermaker as our sole source of potable water. I think it’s worth mentioning that our routine has never failed in all that time. We’ve never once had to resort to dockside water. Allow me to elaborate on what I consider to be the main advantages of such a routine:

  • If the watermaker is run every 2-4 days, you’ll probably never need to biocide it, even in tropical environments. Keeping water flowing through the membrane every couple of days denies bacteria the chance to adhere to the membrane surfaces and multiply.
  • You’ll be able to respond quickly to any problem that might arise, giving you a chance to correct the problem before you’ve exhausted your supply of potable water
  • With a regular source of potable water, you can reduce the amount of tankage needed to store water. In our case, we even converted one of our two original 30-gal. water tanks into storage for dry goods

In summary, our approach to handling our potable water requirements is an integrated philosophy—we are able to produce all the water we need, run the watermaker often enough to keep it happy and avoid having to biocide it, always have a reasonable amount of emergency supply on hand, and free up valuable storage space by reducing our allotment for tankage. There is, however, another common philosophy that is just about as opposite to ours as you can get.

Several years ago, in the pre-Katadyn days, the then-product manager for Recovery Engineering visited me at Loreto Fest, a great cruiser party held each spring in Puerto Escondido, B.C.S., Mexico, hosted by the Hidden Port Yacht Club. He was attending to help the yacht club raffle off a new 40E watermaker which Recovery Engineering donated each year to help the club raise money for its charity work in the area. During his visit, he told me of a problem he had encountered at recent boat shows, when he was representing PUR watermakers. The competing watermaker vendors, he complained, were all giving out similar advice, which went something like this: “You should buy one of our large capacity watermakers. Since you need to run your engine anyway to charge your batteries, freeze your refrigeration cold plate, etc., you can make all the water you need at the same time and store it.”

The product manager didn’t have a come-back for that argument and wanted to know what an experienced cruiser like me thought about it. I told him I estimate that probably more than 80% of the cruising fleet that heads south from the United States and Canada to Mexico every fall are taking their first long trip, usually on relatively new boats. Of those who make it, I also estimated that three-quarters of them make their way back to the States and never make another trip. The cruising life is not for everyone and “experience” comes slowly—and sometimes painfully. A large percentage of new cruisers do not have enough technical knowledge to understand their equipment. That’s why the arguments of the vendors of large watermakers seem appealing. They were usually “looks good on paper” statements from salesmen, with little or no cruising experience, made to novice boaters. My experience leads me to consider several serious flaws in that “big gun” philosophy:

  • A vessel’s main auxiliary engine should not be run on a regular basis at less than 25% of its rated full load—any competent diesel mechanic can tell you that. The low heat level, excessive accumulation of carbon deposits from incompletely burned fuel (wet-stacking), and accelerated accumulation of sulfur byproducts in the oil, all have a detrimental effect on the engine and will substantially shorten its useful life. Even when charging the batteries with a high-output alternator, cooling a cold plate, and running a watermaker, the total load is likely to be well below 25% of the engine’s rated full load. This is even more likely with the larger engines commonly found in newer cruising boats
  • Making a large amount of water at one time means that there are likely to be extended intervals of time between runs. Since the watermaker should be biocided if not used within the next 3-4 days (according to my philosophy), proper watermaker maintenance would dictate biociding after every run. This is especially true in warm, tropical environments where the rate of bacterial growth on the membrane surfaces is greatly accelerated
  • Large amounts of product water needs to be stored. In many cases, this will require large water tanks, thus defeating the advantage of being able to free up storage space

Whatever your own thinking on this subject, the first step is always to realistically estimate your water needs. If you have half a dozen people aboard who are avid divers and need to rinse down several wetsuits and diving gear every day, you’re not likely to be satisfied with a small watermaker. On the other hand, if you are two people on a smaller vessel with modest water needs—well, that’s who the Katadyn 40E was designed for. The main point is to choose a watermaker size that allows you to run it regularly and often. Remember: watermakers, like most other equipment, want to be used. They stay happier that way.

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Prefilter Service and Avoiding Rotten Egg Smell:  In my article on installation of a 40E, I strongly emphasized the need to locate the prefilter assembly in an easily accessible place. Now I’ll discuss why that is so important.

The primary purpose of the standard 30-micron prefilter element is to block the passage of any particles of material in the input seawater that are larger than 30 microns. Smaller particles that get by the prefilter are small enough to flow through the membrane without becoming lodged. The prefilter’s role is simply to keep the membrane from eventually becoming plugged up with flotsam.

The larger particles of flotsam that are stopped at the prefilter, of course, accumulate in the filter bowl and stay there until removed. Depending on the quality of the intake seawater, the rate of accumulation can be slow or surprisingly fast. Usually the rate of accumulation is very slow when using open ocean seawater for the intake. The opposite occurs when making water in an anchorage close to shore (which is where most cruisers spend 90% of their time!). In any case the debris trapped in the prefilter bowl consists of many different kinds of material. Some of it is organic—e.g., plankton, grass, small marine animals.

Many people just learning to use a new watermaker initially believe that they only need to change the prefilter element before it gets fouled enough to impede the flow of intake water. Of course, this is true as far as it goes. Unfortunately there’s another consideration of even greater and more immediate importance—typically, long before enough flotsam has accumulated to interfere with seawater flow through the prefilter, the organic material that has already been trapped will start to decompose. This happens even more rapidly in tropical environments—it will become a problem in just a couple of days. The telltale symptom is a “rotten egg” smell in the product water the next time the watermaker is run. When this happens, you may find it necessary to run the watermaker for an hour or more before the smell disappears.

The reason is that one of the products of the decomposition of organic material is hydrogen sulfide, which smells like rotten eggs. In concentrated amounts, it’s a very deadly gas that can kill you in a heartbeat. It’s a common, and serious, problem for oil field personnel working with crude oil that has a high sulfur content. However, the concentrations found in your watermaker product water are too small to represent a hazard. The problem is the noxious smell. The first time you experience it, you’ll probably think there’s something wrong with your watermaker.

You might wonder why the watermaker membrane doesn’t remove the hydrogen sulfide. The reason is that the hydrogen sulfide molecule is very small, comparable to the size of water molecules, and easily passes through the membrane along with the product water. It’s interesting to note that in the very early days at Recovery Engineering, even the customer support people didn’t understand the nature of the problem. If a cruiser contacted them to complain about a rotten egg smell in the product water, he was likely to be told that the membrane probably needed replacing. Clearly, that was an expensive—and ineffective—solution to the problem.

The real solution to the rotten egg problem is actually very simple: change your prefilter element often; i.e., keep it clean! I religiously change my prefilter element every time I run the watermaker. At this point, an alert reader may ask: “Since you recommend running the watermaker every 2-3 days, doesn’t that add up to a lot of rather expensive prefilter elements?”—and that’s an excellent question. At a retail cost of about $10 per filter element, my method would seem to be a real budget buster. However, there’s a trick to it. I use two filter elements, which I swap back and forth. Here’s the technique fully explained:

Run the watermaker and produce the quantity of product water that you need. At the end of the run, remove the prefilter element, dump out the foul water from the filter bowl, clean it out with a rag or paper towel, and install the second filter element. Then tie a line through the center of the dirty element, toss it over the side of the boat so that it hangs underwater, and tie the other end of the line to a lifeline or other secure place. Let the dirty filter bob and dangle in the water for a few hours or overnight, or tow it behind the boat for 10-15 minutes if you happen to be underway. Finally, retrieve the old element and set it somewhere exposed to the sun for a day or two. The next time you do a watermaker run, repeat the process. By the way, if you have a coarse seawater strainer installed inline, you should realize that it is subject to the same problem caused by accumulated flotsam—the crud is the same kind, just bigger chunks. Don’t forget to clean it regularly too.

I realize that, at first, this seems to be a lot of work, but it really isn’t. I think of it as a good habit to develop, like brushing your teeth. I don’t like what seems to be all the time wasted in brushing my teeth every night before going to bed, but I do it because keeping my teeth in good shape is important to my lifestyle. If your watermaker is important in your cruising lifestyle, as it is in ours, you’ll soon find that this prefilter maintenance habit only takes a couple of minutes and will go a long way toward assuring you can produce consistently high-quality product water every time you run your watermaker.

There’s an added benefit to this procedure. The longer you let the prefilter element go without changing it, the dirtier it gets and the harder it becomes to clean it. Eventually it will get so fouled that you’ll simply have to discard it. That’s $10 out the window. If you follow my advice and swap out the filter element every time you run the watermaker, it will be easy to clean it with a short towing or an overnight period of bobbing in the water at an anchorage. Even better, the element will last a very long time. We typically make a pair of filter elements last for six months to a year, even though we use our watermaker almost daily and produce all our potable water. A last word of advice: don’t try to scrub the prefilter element to clean it. Doing so doesn’t clean the element much better than the method I’ve described, but it will raise and tear the filter fibers and significantly shorten the useful life of the filter element.

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Pump and Drive Unit Maintenance:  The pump and drive unit don’t require much in the way of regular maintenance. If the watermaker develops a squeaking sound when running, try applying a little silicon grease to the exposed drive shaft. Check the pump and drive unit occasionally for leaks. Contrary to the information in the original PUR Owner’s Manual, the watermaker pump should not leak—not at all! If a leak develops, something’s wrong; find it and fix it!

The electric motor is industrial quality and very robust. You can expect it to have a long life. The brushes should last well over 5000 hours. If you have a unit with removable brush caps, you can check them every few thousand hours. I’ve been running one of my watermakers for almost 10,000 hours and the brushes still have plenty of life. In the event that the motor fails for some reason, there are lots of repair shops that specialize in the repair of electric motors, even in the third world. If you’re in a remote location, taking the motor to a local repair shop is usually advisable—certainly cheaper and quicker than sending the motor back to the States for repair. Get on the local VHF radio net and ask for recommendations about a local who is known to do good work.

The gearbox should probably never need any attention, unless it develops an oil leak. In the couple of cases I’ve seen of an oil leak from the gearbox, the leaks were there from the outset and the units should have been immediately returned to the factory for warranty repair. I’ve not yet seen a gearbox that has developed a leak later, out of the blue. The Repair Seal Kit from Katadyn (something you should always have on hand) includes a bottle of gear oil for the gearbox. I personally do not recommend changing the gearbox oil at every routine Repair Seal Kit servicing. I see no reason why it’s necessary. If you want more information about this, I’ve explained my reasons in the Repairs Video.

The pump itself should easily run for at least 1000 hours with no problems, at which time both I and the factory recommend installing a new Repair Seal Kit. The Repairs Video on this CD provides a detailed explanation and demonstration of this procedure. The greatest value in performing this servicing routine is in cleaning the watermaker and inspecting all the working parts. In most cases, you’ll find that many of the seals are still in excellent shape and don’t really need to be replaced. Pay special attention to the two large pump body o-rings, the piston shaft seals, and the seals on the piston head. These are the seals that work the hardest and are most likely to need replacement.

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Biociding the Membrane:  Treating the watermaker with a biocide (also known as “pickling”) has a single purpose: to kill bacteria in the membrane. It is a procedure that is necessary whenever the watermaker will not be used for an extended period of time. The original PUR manual recommended biociding the watermaker if was not going to be used within the next week (seven days). This specification was developed by factory people who lived in a temperate climate (Minnesota) and were relatively unfamiliar with environmental conditions in the tropics. Based on my own experience, I recommend that, if you are using your watermaker while in tropical climates, you should biocide it if it’s not going to be used within the next 3-4 days. My reason for recommending this shortened time period is that bacteria multiply much faster in warm environments like the tropics. Better to be safe than sorry.

The chemical used as a biocide in the original PUR—and the early issues of Katadyn—watermakers was sodium metabisulfite. It works as an antioxidant, which means it has the ability to absorb oxygen from its environment. When a solution of sodium metabisulfite is pumped through the membrane, it removes the oxygen inside the membrane. Since the bacteria are aerobic, and need oxygen to live, they are killed when subjected to such a solution. Sodium metabisulfite is commonly used as an anti-bacterial agent in restaurants and the wine industry.

Several years ago, Katadyn changed their biocide chemical. I have no reason to believe that the new chemical is not just as effective as the original sodium metabisulfite. Perhaps it is even more effective. Unfortunately, I’ve not been able to learn exactly what its chemical composition is or how it works. It is my understanding that the change was made for ergonomic reasons. Sodium metabisulfite can irritate mucous membranes. Apparently the new chemical doesn’t do that and is, therefore, more “user friendly.” On the other hand, there is no reason to believe that the original sodium metabisulfite is not still perfectly effective. If you have a source for it, don’t hesitate for a moment to use it.

Biociding your watermaker should be done whenever you’ll not be using the watermaker for an extended period of time. If the watermaker is going to be laid up longer than a year, the factory recommends that you should biocide it annually. I’m not convinced that this is necessary, but it can’t hurt. Again—better safe than sorry. However, my thought is: once the bacteria inside the membrane have been destroyed, why should it be necessary to destroy them again, unless more contaminants have been run into the watermaker in the interim? Use your own common sense; if you’ve biocided and stored your watermaker for 14 months without another biociding treatment, I wouldn’t worry too much about it. I’ve actually seen some old Model 35 watermakers that had been laid up for several years after a single biocide treatment, and I was able to bring them back to productive life with no problems.

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The Acid and Alkaline Cleaning Processes: Katadyn supplies two types of membrane cleaning chemicals with each new watermaker. More of these chemicals are included in the Extended Cruise Kit. The Acid Cleaner is intended to remove mineral scaling from the inside of the membrane. The Alkaline Cleaner is for removing organic residues, such as accumulated bacterial films.

I’m not a big advocate for using these chemicals on any kind of a regular basis. Basically, it’s been my experience that they rarely—if ever—do any good. After servicing hundreds of watermaker problems of every description over many years, I can’t remember one instance where cleaning the membrane solved a problem or even made any difference at all.

The Acid Cleaner, in particular, seems useless. It’s designed to remove mineral scale from the membrane surface. This is, indeed, a common problem with industrial RO plants that are processing inland raw water sources, where there are frequently substantial amounts of minerals dissolved in the intake water. In those cases, regular cleaning of the membranes with such chemicals is clearly necessary. However, the small amount of dissolved minerals in seawater is not a problem. Unless you happen to be using your watermaker to process inland water sources that are known to contain minerals, you will probably never need to use the Acid Cleaner.

The Alkaline Cleaner, on the other hand, may have some occasional use for the typical Katadyn watermaker owner. If you’ve let your watermaker sit unused for a long time without having biocided it, there’s a good chance that the membrane will have some serious bacterial growth on the inside. That’s about the only situation I can imagine where an Alkaline Cleaner treatment might be recommended. Instructions for performing the cleaning processes can be found in the Katadyn 40E Owner’s Manual, by following the link on the navigation bar. I’ve also included some more comments on this subject in the Troubleshooting article, which is also accessible from the navigation bar link.