We have a Village Marine STW-600 watermaker that nominally produces 25 gallons per hour. We use it heavily and, over the last 11 years, we have wound up just over 2,000 hours on it. Since the watermaker is such a mission critical component for us, we wanted to have lots of spares on board so we took the unusual move of purchasing a used Village Marine industrial unit when our boat was new. Even though the industrial system looks very different, it shares all the important components.

The system has been very reliable over the years. We had a salinity probe fail in 2013 and that was the first time we used parts from our spare unit. Then in 2015, our membranes were really struggling to produce even 800 PPM (parts per million of total dissolved solids) water quality. (Seawater starts at about 30,000 PPM and, according to the Safe Drinking Water Foundation, below 900 PPM is fair quality, below 600 is good and below 300 is excellent). So we used parts from the spare system a second time and put in three new reverse-osmosis membranes.

From 2015 until 2020, we’ve done nothing with the watermaker except use it. And we have used it a lot. There are now just over 2,000 hours on the system.

It’s pretty amazing to go a decade and in 2,000 use hours replace only a salinity probe and the membranes. But a few weeks prior to this service, we started to encounter serious watermaker problems. Sometimes when it was turned on, the inrush current would shoot up over 30A and then it would either pop the 20A breaker or settle back down to normal current draw and make water without issue. We used the system like this for several weeks but it was clearly getting worse and it often took 3 to 6 tries to get it to successfully start.

In thinking through the inrush current problem, there seems to be three possibilities. It might be blocked inside and the positive displacement pump was blocked, preventing rotation and causing massive inrush current. Given that the system worked fine when it did start, it seemed unlikely that it was blocked. The two more likely diagnoses were a seized pump or a failed motor.

We checked the oil level in the pump and it was correct and the oil was clean. Clean oil suggests the pump is not seizing up and instead the motor likely is at fault. And, whether the problem is caused by the pump or the motor, both have to come out prior to servicing either of them. So it doesn’t really matter which is the cause of this problem.

  

Changing the High Pressure Pump Motor

The watermaker is in the aft starboard corner of the boat and like many places on a small boat, it’s not the easiest to access. But, over the last 10 years, the only scheduled maintenance where we need to back here is the annual filter changes, so the location has worked out fairly well.

What we don’t like is the all-in-one one design rather than a modular system. These look nice and neat, but taking the pump or motor out is a real struggle where the system has to be unbolted from the deck, hoses removed, the system lifted to access the pump/motor bolts, then both have to be worked out the back. It was time to get to work.

The first step in this service operation was to disconnect the hoses to allow the chassis to be lifted above the deck for to access the pump/motor hold-down bolts. It’s fairly easy to then lift off the three R/O membranes, after first removing the bolt at each end that holds them to the chassis. This exposes the motor/pump assembly.

After lifting the three membranes free, we put them up on deck as a unit just to get them out of the way and allow better access to the rest of the watermaker.

The watermaker is held down by 8 quarter-inch bolts, 4 along the front and 4 along the back where some of the front bolts can only be accessed by removing the electrical panel. When re-installing the watermaker we used only five quarter-inch bolts which is adequate and avoids having to open up the electrical panel to attach or detach the watermaker chassis from the floor.

For all service other than pump/motor assembly removal, the chassis can be left in place. But since the motor is bolted through the bottom of the chassis and the nuts are not captive, the watermaker must be fully removed from the floor and then lifted high enough to access the pump/motor attachment nuts.

Above you can see that we’ve had to remove the electrical panel to find the last of the watermaker hold-down bolts. Once that was done, we had to lift the system to access the bolts securing the chassic to the pump/motor assembly.

The system weighs a bit more than 100 lbs and there isn’t enough access to easily lift the watermaker so we used wooden wedges to push the assembly up and allow access to the pump/motor nuts. On the right above the chassis has been lowered back to the deck, and the pump/motor assembly has been worked out the back. The pump/motor clearance is so tight that the motor grease nipple even needed to be removed to have sufficient clearance.

Once the pump/motor assembly has been removed from the watermaker, we could lift it up onto the back deck for easy service. Above on the left the spare pump and motor are in the foreground and in the background are the pump and motor we’ve just decoupled. The pump housing attaches to the motor housing using 4 bolts and motor shaft drives the pump through key slip connection locked in place with an allen headed bolt. The shaft needs to be rotated until the allen head bolt is visible in the service opening.

We now had the faulty pump/motor assembly split into individual components. We drained the oil out of the high pressure pump and it looked great. The pump bearings felt great and, from experience, we know that if the breaker stays engaged after starting the watermaker, it would make water for as long as needed. We’re just about positive we have a good pump and, since it’s all that is left, the motor is faulty.

On the right above, we are re-attaching the spare pump onto the existing high-pressure pump. This motor is wired in slightly differently so we needed to make some wiring changes but, once that was done, the pump/motor assembly is ready for re-installation into the chassis.

One of our pet peeves with installers is that, in the search for a nice clean look, they don’t leave service loops and access to connections. As a result, easy jobs can take much longer. Here because the manufacturer didn’t use captive nuts to hold the pump/motor assembly, the entire watermaker needs to be lifted to access the pump/motor attachment nuts. Because there is no service loops, many hoses must be disconnected.

The hose connection circled above was particularly difficult during reassembly. The hose comes up through the floor directly into a 90 degree fitting. The hose is too short to pull up and attach to the watermaker when the watermaker is lifted above the floor. Instead, the 116-pound watermaker needs to be gently lowered onto the hose. But, of course, the hose just pushes down into the floor rather than sliding onto the hose nipple.

The easy answer would be to secure the hose below the floor and lower the watermaker and the pipe nipple into the hose. Unfortunately the hose can’t be accessed from below. We eventually found the solution was to put a small wedge between the hose and the deck hole to secure the hose in place and then lower the watermaker down onto the hose, tighten the hose clamp, then remove the wedge and lower the assembly the rest of the way. Lack of a service loop transformed a 3-minute job into a 45-minute effort.

Above on the left is the re-installed motor/pump assembly from above and on the right is the assembly viewed from the back of the watermaker. It’s a tight fit.

As part of this service operation we also intended to change the membranes and do some other service operations, but we want to test the motor change first. Here we have placed the membranes assembly back on the watermaker and reattached the high pressure and low pressure hoses so the system is now ready to test.

It worked great and now starts and operates exactly as it should.

  

Faulty “Check Unit” Indicator Light

The next service operation was to correct a fault that has been around for six years. The water maker tracks service intervals and reminds the operator when works needs to be done by illuminating the “Check Unit” light. This is a nice but not necessary feature and six years ago it stopped working. The light is usually always on, whether it needs service or not, but it sometimes goes out. What’s happened is the NVRAM on the main circuit board is faulty, so the system maintenance intervals are random numbers and the result is the light is usually indicating service is required.

In the picture on the left above you can see the used system we bought for parts is very different from our watermaker pictured earlier, with all the control electronics held in separate junction box. But, the electrical panels appear to be the same. On the right, we have removed the electrical panel from our water maker. We believe this is the faulty unit.

On the left, we’re tearing down the electrical junction box from the “donor” used watermaker we bought for parts. Once we got it open we could see the board was the same and the EPROM was running the same version of firmware so we’re pretty confident we can use this board to replace the one I just removed from our watermaker with the faulty “check unit” indicator light.

On the right above, the new board installed and it tests out well. Everything works as before and the maintenance tracking system is back to working again. That’s two problems solved now.

  

Changing Membranes

With just over 2,000 hours on the system, the watermaker was due for its second membrane replacement. The first set lasted about four years in heavy use and this current set has gone just over six years. Given that we run 175-200 hours per year, this feels like excellent membrane life.

Above on the left, we’re unpacking one of the three new reverse osmosis membranes that we purchased some time back, knowing we would need them eventually. These are shrink wrapped in the manufacturer’s pickling solution.

On the right, you can see the three new membranes and spare membrane pressure vessel end caps. It’s highly unlikely that we’ll ever need the spare end caps, but the ends caps are a remarkably tight fit in these pressure vessels and considerable force is needed to disassemble or put back together. So we keep the spare end caps around in case we damage one.

Removing the end caps requires first removing the allen headed cap screws. Then, using a large blade screw driver or small pry bar, the process is to gently work the pry bar into the notch between the pressure vessel and the end cap. There is a notch on each side so gently work one side and then the other until the end cap comes out. Be careful not to damage the O-ring or even touch the sealing surface on either side of the O-ring with the pry bar.

Most people remove both end caps, but we find that we only need to remove the cap on the side pointed to by the blue flow arrow (visible in the picture on the left above). On the right, we’ve got the end cap off and have pulled out the old membrane (visible in the foreground). We’ve partly installed the new membrane and are lubing the O-ring with the silicon lubricant Village Marine supplies with the membrane. Once that is done, we gently slide the membrane into the pressure vessel.

Once the membrane is back in the cartridge, the end end cap needs to be reinstalled. These caps are really tight and this can be a tough task but there is a trick that makes it easy. In the right bottom picture above you can see we have the short cap screws that hold the end cap on but we also have a set of longer cap screws. We use these longer cap screws as a press.

The trick is to put the end cap on, just resting on the pressure vessel, and install the longer screws finger tight. Then tighten these screws a half turn at a time and they just gently pull the end cap nearly into place. Then remove the long screws and put the short screws in to complete the job and pull the end cap into its final operating position.

This process is easy, fast, and not hard on the equipment.

Before heading back down below we reattached the high pressure pipes and low pressure hoses to the membranes and then took the assembly below for reattachment. At this point, our cat Spitfire decided he needed to do a spot inspection before the membrane assembly gets installed. Once he was satisfied, we placed the membranes on top, attached the hoses, and installed the two membrane hosing hold downs to complete the job.

Above on the left the system is fully back together and we’ve powered it up and it’s ready for testing and commissioning. It’s important that the pickling fluid from the new membranes not go into the water tanks, so we plumbed in a garden hose temporarily to discard the water for the first hour after a membrane change.

It’s great to fire the system up and see it making high-quality water at 25 gallons per hour.

After an hour of running water over the side, we plumbed the system back into the water tank and it’s now making water at 127 PPM, which is excellent quality water.

On the right you can see we were even better in the next anchorage at 86 PPM, but it’s not really improving. The second anchorage had quite a bit of freshwater flowing past us so we were operating on brackish water. There is no problem using a watermaker to make water in brackish or even fresh water. In fact, it’s a good idea since RO will filter out any dangerous pathogens that can live in freshwater.

The only thing to keep in mind when operating a watermaker in freshwater is make sure it’s not producing greatly more than its rated flow. Most systems have flow indicators on the front. If you find the flow is too high, simply reduce the pressure. So, for example, if our 25 GPH system is producing much more than 25, we would reduce the pressure to get optimum membrane life.

We are back to a fully-operational watermaker. It’s already run nearly 100 hours since the overhaul and it’s performing very well. It was a fair amount of work but it’s been 10 years since the system was new so it feels reasonable, especially in light of the fact that we average more than 200 hours of watermaker operation per year. That’s about 5,000 gallons per year which seems excessive. But we operate our boat like a small apartment using the dishwasher daily. We wash the tender and flush the motor when we are done with it, wash the boat when it needs it, do weekly laundry, and have freshwater flush toilets. And so, with our normal personnel water consumption, it all adds up.