Caring For and Maintaining Your Water Maker
Most water making equipment on yachts and boats today use the reverse osmosis technique for converting sea water into drinking water. These RO systems remove solids, bacteria and most viruses from the water, and the water produced is often better quality than water from a city water supply. We all use a considerable amount of water so fresh, clean water is a ‘must-have’ for those folks who plan to be on anchor or away from a good water source for an extended period of time.
Today’s yachts and boats will often have a washer and dryer on-board which can use upwards of 20 gallons of water during each washing cycle. Longer showers, doing the dishes, fresh water toilets, and boat cleaning all add to large amounts of fresh water consumed by today’s boating travelers.
A good rule-of-thumb for water consumption is 20 gallons per day per person. A reliable water maker, producing 20 – 30 gallons per hour will more than handle the requirements of 2 - 4 people on the boat. The key word there is ‘reliable’. While most systems start out as dependable, reliable equipment, neglect or improper use can soon make the system problematic.
Two factors can severely limit or destroy a water maker’s ability to produce ample quantities of clean drinkable water. Those two factors are:
- Exceeding the maximum operating pressure range
- Lack of proper flushing after every water making cycle
There are a few other aspects of operating the water making equipment that will improve the life of the system, but those 2 factors are paramount.
Let’s discuss why keeping the pressure within the limits is important.
Most systems are designed to operate at 800 psi of back pressure. Excessive pressure, even for a few seconds can cause issues within the pressure side of the water maker system. While most membranes can be pushed a bit above 800 psi, the o-rings in the end caps and the hydraulic seal on the membrane are pushed to their design limits when the 800 psi is exceeded.
If the hydraulic seal on the membrane leaks-by or fails, the system won’t be able to build pressure so water production volume can be affected or in some cases if the failure is substantial, it will not produce any water. Reducing the pressure will usually allow the hydraulic seal to hold the pressure, but every time the pressure exceeds the seals ability to hold pressure, a little damage is done which be an issue down the road. Although failure of the hydraulic seal will limit the amount of water produced, you will not produce bad water because
of that failure. Bad water can be described as any water with a TDS (total dissolved solids) reading greater than 500 ppm. (parts per million). We are not going to get into a TDS discussion here but the EPA suggests we don’t consume
water having a TDS above 500 ppm, so we’ll use that number as the maximum acceptable level of dissolved solids.
If the o-rings in the membrane housing end caps leak-by or fail, the system WILL produce water that has excessive dissolved solids. When those o-rings leak or fail, raw water is allowed to enter the fresh water side of the system which is down the center of the membrane, then directly to the fresh water tank. The entire tank of fresh water can be contaminated in a matter of minutes. We have seen o-ring leak-by cause a TDS reading to jump from 190 ppm to 840
ppm within a few seconds. There are typically 2 o-rings in each end cap so the redundancy should protect the system, but excessive pressure can damage them. Failed o-rings will also impede the system’s ability to come up to operating pressure. Those little o-rings are all that stand between you and bad water.
Excessive pressure spikes can rupture or damage the interior of the membrane which will then allow raw water to enter the fresh water side of the system. Although this is rare, repetitive pressure spikes can cause a rupture. After you have set the pressure, it is a good idea to monitor it because pressure can have momentum in some systems and we have seen pressure continually increase as the high pressure pump comes up to operating temperature. We recommend an initial setting of 725 psi – 750 psi as a safeguard against that increasing
Remember, raw water contains bacteria and possibly viruses in addition to salts and minerals. These are all normally removed by the RO process. If the water from your water maker tastes salty or is discolored, raw water, including bacteria is likely getting to your tank.
Most water making systems on smaller boats are described as ‘manually operated and monitored’ meaning the operator has to turn on pumps, move levers, adjust valves and monitor water quality during the water making process. Monitoring the pressure, water quality, and production rate are important to the longevity of the system and more importantly to the health of anyone who will consume the water. It might be boring to sit there and stare at the pressure gauge and water quality meter, but your system will last longer and your health
depends upon good, clean water is sent to the tank.
Why flushing is important.
Remember that the RO process removes the solids, bacteria, and most viruses from the raw water so you only get good quality, clean water. As the system is producing good water, the ‘stuff’ taken from the water is dumped overboard after it flows out of the membrane housing. However, at the end of the water making cycle, when the pumps stop, whatever raw water is remaining in the membranes, tubing, pipes, and pumps still contains those solids, bacteria, and viruses. In addition, the membrane is a structure with lots of little crevices where bacteria can hide. If the water making process is stopped and the equipment is not flushed out, those left-over bacteria and viruses can grow which can limit your system’s ability to produce water and
possibly get through the membrane into your water system.
Flushing after each water making cycle will push most of those contaminants out thus protecting your system. Some folks believe that making water every couple days negates the need to flush. We don’t subscribe to that thought process and believe that the continual buildup of contaminates will lead to a shortened membrane life. Since the membranes are one of the most expensive components in the system, and are time consuming to replace, we prefer to do everything we can to extend the life of the membrane(s). Keep in mind that flushing uses fresh clean water from your tank so make sure there is at least enough water in the tank to complete a flush. Typical systems will need 4-8 gallons of fresh water to properly flush the entire system.
If your system is to be dormant for an extended period, regular flushing will limit the growth of bacteria and viruses. We normally suggest a once per week flush of a system that is not being used. If the system has been dormant for more than 14 days, even if you have been flushing it every week, we recommend two successive flushes prior to making water as a precautionary measure. The other option is to pickle the system to keep bacteria and viruses from growing but that should be a last resort because of the potential problems pickling can cause. We’ will discuss pickling a little later in this article.
A good quality Ultraviolet Light, located at the output from the water maker will ensure that 96% of any bacteria and viruses that get through the membranes are killed or are dormant before they enter your fresh water tank. However, the UV light will not remove solids and minerals so if you have a membrane or o-ring failure the water should not be consumed.
Let’s look at a few other things that need attention to extend the life of the water maker. The voltage source connected to the water maker should be monitored periodically to ensure a proper voltage level is maintained while the system is operating. Some users operate their water maker on an inverter which is drawing current from a battery bank. Depending upon the quality of the inverter and the batteries, you’ll want to make sure the voltage is within the
specifications of the water maker system. For example: A water maker with a rated voltage of 120 volts is going to draw excessive current if the voltage supplied is only 105 volts. Current in the pump motor will increase which will
generate more heat thus shortening the life of the motor.
There should be a couple sediment filters before the high pressure pump. These filters remove debris which could cause problems with the high pressure pump. If these filters become excessively dirty, the high pressure pump will starve and won’t be able to build pressure. We have seen one system where the filters were clogged to the point of not allowing any water to reach the high pressure pump. The pump was ruined because the high pressure pump could not tolerate running dry.
When adjusting the pressure valve, raise the operating pressure slowly, allowing the pressure to settle at several points along the way, before continuing to reach maximum. Raising the pressure too quickly can rupture the membrane or those little o-rings we discussed earlier. When starting the system, the feed pump should be allowed to run for 15-30 seconds before activating the high pressure pump. Then allow the high pressure pump to run for 15-30 seconds to allow air to be purged from the housings and the lines. Membranes don’t tolerate
high pressure air bubbles and can rupture.
Pickling your system
Water makers that are not used for extended periods and cannot be flushed weekly can be pickled. Pickling uses Sodium Metabisulfite to inhibit bacteria growth. Pickling works very well but it can cause issues.
Some owners believe that if the water maker is pickled, the system can be left untouched for years. Although theoretically this is true, we have seen many cases where the pickling material has dropped out of solution and become caked on membranes, pump internals, and valves. When this happens, the component is usually ruined. One of our owners is a Marine Surveyor who has seen dozens of situations where a water maker has been pickled for 6-12 months, and the pump is now locked up or the membrane is clogged. Sometimes flushing can push out the caked pickling material but in most cases the owner has to replace the pumps and/or membranes.
If you are not going to use your system for a long time, there are 2 other options.
The first choice is to remove the membranes and flush the pumps and lines with fresh water. Bacteria can still grow in those lines but if the system is open, allowing air to enter the lines, it is less likely. Exercising the pumps and valves once per month will help ensure those components are usable and healthy.
A better option is to purchase the preservative, lubricating, and cleaning cartridges that are sold by a few companies. These are elements that go into your sediment filter housing, then you simply run the system to distribute the chemical in the cartridge. Again, exercising the pumps and valves is still recommended to make sure those mechanical components are healthy when you want to reactivate your system. Applied Membranes sells these cartridges that will help keep your system healthy. We have no affiliation with this company.
Water makers are an expensive investment. Caring for that investment will make sure the system performs as you expect it to.