7 tips on maintaining a reverse osmosis (RO) watermaker
Last updated: 24/04/2017
A reverse osmosis (RO) watermaker has become an increasingly more important piece of equipment on board a vessel. However, like most equipment, marine water makers need maintenance. Luckily, RO watermakers only require minimal amounts of maintenance to keep them in a healthy state and prolong their lifespan.
Below is a list of simple maintenance procedures all owners of water makers should complete after around 500 hours of usage. The example is based on a small to medium sized RO watermaker producing 8 to 15 litres of water an hour.
Keep the watermaker membranes wet and healthy
Very importantly, you have to keep the membranes wet. Leaving them to dry out will reduce the lifespan of the membrane drastically. To do this, you simply should run it once every week as a minimum. An RO watermaker doesn't like to sit still.
Some RO watermaker systems have an automatic feature called a 'fresh water flush'. This means that it automatically flushes the desalinator with fresh water. However, that typically only works when the electricity supply to the water maker is continuous.
If, for whatever reason, the boat’s power goes out and then back on, the timer may start from zero, meaning the watermaker may not fully complete its flush.
This is also a good time to test the fresh water flush line to make sure that the water from the fresh tank reaches the water maker during the flush cycle. This ensures that there are no valves inadvertently shut or any lines obstructed.
Replacing filters in an RO watermaker
An RO watermaker needs an ample flow of water, which means keeping the pre-filters working properly.
As the filters clog up, supply pressure drops; there is a gauge on most RO water makers to monitor this. Some operators check the pressure daily and change the filters when it falls below a certain point, while others largely ignore the gauges and wait until the system’s low-pressure cut-off stops the system. Both ways work, but the latter results in lower freshwater output during the final stages before the filter is changed.
Regular replacement is recommended for overall lifespan of the unit, which can also mean the system is more reliable during longer periods of use, where the filter may not be able to be changed as often as you usually world.
Use good quality water filters
When changing filters, resist the temptation to use less expensive pool or spa filters; even if they might fit. Such filters are most likely going to be made of paper and will fall apart under hard use and high pressure. The recommended pre-filters are often only slightly more expensive, but they can last about five times longer under the same conditions.
Check your watermaker for leaks
By cleaning and wiping an RO watermaker with a moist rag, you are able to spot both water leaks and oil from the high-pressure pump. Finding salt residue would indicate a leak of some sort and these can often occur because of the vibration of a typical system.
The watermaker system is, like everything on board, subject to vibrations transferred from the vessel and the equipment. In the event of a suspected leak, all of the RO watermaker mounting hardware should be inspected for tightness. Inspect all screws, brackets, nuts, bolts and fittings. Pay special attention to the high-pressure pump and motor since this will often be subject to the most vibration.
Clean and check the salinity probe
It's a good idea to check the salinity probe or salinity metre, to ensure its accuracy. This measures the degree of saltiness in the product water and makes sure that only clean filtered water goes to the fresh water tank.
To do this, simply unscrew the probe anti-clockwise; check if it is clean and free of any debris. Use a soft bristle brush if there is any debris built up on the probes, clean its thread and then screw it back on clockwise.
If in doubt of the salinity probe’s accuracy, pocket salinity metres are available to cross-reference your results. It’s often a good idea to have a backup, anyway.
Change the crankcase oil
The high-pressure pump has an oil reservoir that is very important to check after the first 50 hours, and then again every 500 hours of usage. Most watermaker manuals state when to do an oil change, so read your water maker manual to take note of what the recommended time is.
Changing the crankshaft oil is very straightforward. Purchase the recommended oil from the watermaker’s manufacturer. Open the oil cap so it can vent and on the bottom side of the crankcase, there will be an oil drain plug. Turn it anti-clockwise, until the oil drains in the little flat container you have put under it.
When all is gone, close the drain plug and fill the crankcase with new oil until you have reached the recommended level. Then close the oil cap; when the water maker is turning, check for leaks.
Run a full test after any watermaker maintenance tasks
It is best to test any RO watermaker in open-ocean conditions after any kind of maintenance or repair, where the seawater is exposed to good tidal exchange.
Back the pressure regulator off all the way (turning it anti-clockwise as far as it will go). Start with low pressure on the system and let seawater circulate through for about 10 to 15 minutes. During this time, visually inspect the system, all components and all hoses, to make sure that there are no leaks or other abnormalities.
Confirm the feed water inlet pressure is in the approximate range of 20 PSI to 40 PSI after this period of time; gradually increase the pressure until the system is making its rated water output.
Check the system’s operating pressure, feed water TDS and system output. If the system comfortably makes its rated product water output, the watermaker should be fully functional, healthy and efficient.