Steve -

My water maker suddenly stopped producing water. The display shows that the water quality is poor. Up until it stopped working, the water quality was excellent. Is it possible that the water quality has gone bad so fast, or it likely to be a water quality sensor problem? 

I will presume that the watermaker really did stop working “suddenly”. This does not mean that it didn’t work on one monthly visit, when it worked just fine the month before. This is an important distinction, because time can be harder on a watermaker than heavy use. A month of improper storage can be enough to end the life of your membranes. If your watermaker went from good to bad from one minute (or day) to the next then proceed on. 

It’s possible that the water quality has gone bad very quickly, although it’s more likely to be a quality sensor problem. As usual, the way to proceed is by fault isolation. The first, most obvious step requires a portable water quality tester. Simply test the water that is coming directly out of the membranes. You won't be able to test the water that goes directly to the tank, because the water quality sensor normally controls a valvethat diverts the product water to waste. If you have more than one membrane, check the product water from each. This will alos allow you to determine which of te membranes is at fault. You can tell which of the membrane connectors is the product output very easily. There are normally three connectionsto each membrane vessel. The input salt water and the output brine connectorsare heavy-duty hydraulic style connectors that must handle1000psi of water presure. The output product connector is for low pressure and is often a plastic connector that can be disconnected by hand. Most water makers, in good condition, produce water that will read around 200 ppm TDS (that's parts per million of Total Dissolved Solids). Depending on whose standards you like, the acceptable limit is between 500 and 1000 ppm TDS. Most water quality testers actually test the electrical conductivity of the water, which is then converted into equivalent TDS, assuming the solids are salt.

If all of your product water quality is good, you can re-route the water flow around the automatic waste valve, while you work on correcting the sensor problem. You will have to manually re-route the product water to waste every time you start the water maker, until the product water quality is acceptable. All water makers produce poor quality water for the first few minutes of operation. 

If the water quality is bad, or you don’t have a portable tester; you can proceed assuming that your built-in quality sensor is good. This procedure assumes that you have more than one membrane. Try disconnecting the output water of all membranes except one, while watching the water quality indicator.  This will give you a quality reading for one membrane. Repeat this process until you have a figure for each membrane. DO NOT plug the output of disconnected membranes; the backpressure will damage the membrane. If you determine that one of your membranes is producing the bad water, you can continue operating the water maker with the output of that membrane diverted to waste, while you order a new membrane. Individual membranes do not often fail, while the others are working well. In this case however, the symptom of a drastic quick reduction of water quality that you experienced points to a failure of just one membrane. If you find that all membranes are bad, you should doubt the assumption that the water quality meter is working properly. 

If you don’t have a portable water quality tester, don't worry, there's a lot of fault isolation that you can do without one. If the water quality has suddenly gone out of limits, it's probably bad enough that you can use your taste buds to determine if the water is really bad. Don't try tasting the water if the seawater you are operating in isn't safe for tasting in the first place. You might have raw input water in the product water output. If all of the product water tastes OK, you still might have marginally bad water or you may have a problem with the water quality sensor system.

Diagnosing the water quality sensor system: The water quality sensor works by testing the electrical conductivity of the water. It does this by putting two electrodes into the water flow, and then measuring the electrical conductivity of the water between the electrodes. Before changing anything in the sensor system, manually reconnect the product water flow to send the output water to waste, without relying on the automatic waste diverter valve. This will avoid the possibility of contaminating your tanks with raw seawater.

Disconnect the wires from the water sensor to the electronics. Disconnecting these wires should force a “good” water signal, because this stops all conductivity. If the display does not show “good” then you have a problem with the electronics unit. If the display shows “good” then check the in-water sensor. Remove this from the water flow, and plug the hole. With no water on the electrodes, it should indicate good water. If it doesn’t show “good”, your in-water sensor is bad or just dirty. One of the common problems with these sensors is a crack in the plastic insulating body that holds the electrodes. These cracks become fouled and start conducting.  

If you get to the end of this fault isolation process, with good tasting water, and an apparently functional quality sensor system, it is time to get an independent water quality sensor.

Stephen Sommer is a degreed electrical engineer with extensive experience in electrical, mechanical, refrigeration and air conditioning systems and holds a USCG Masters license. He consults in all areas of yacht systems, which include all the equipment on board yachts beyond a basic hull and motor or sails.

757 SE 17th Street, Suite 237, Ft. Lauderdale FL, 33316

Boatek.com has written articles for  Dockwalk and is a regular monthly columnist in South Winds magazine. To see a current list of our published articles

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