Reverse osmosis (RO) water maker maintenance

Written by Michael Henson | With thanks to Hydro Marine

A reverse osmosis (RO) water maker has become an increasingly more important piece of equipment on board a vessel. However like most equipment, marine water makers need maintenance.  RO water makers only require minimal amount of maintenance to keep them in a healthy state and prolong its lifespan.

Below is a list of 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 water maker producing eight to 15 litres of water an hour.

The hull of a superyacht on the water

Water maker maintenance procedure

Keeping it wet

First of all, 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 have to run it once every week as a minimum. A RO water maker doesn't like to sit still.

Some RO water maker systems have an automatic feature called a 'fresh water flush'- cycle. This means that it automatically flushes the desalinator with fresh water. However that only works when the electricity supply to the water maker is continuous.

If, for some reason, the power goes out and then back on, the timer starts from zero, so technically the RO water maker may not have been flushed for weeks, if it is left unattended like that.

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 RO water maker filters

An RO water maker 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, according to the experts, watch the pressure daily and change the filters when it falls below a certain point, while others ignore the gauges and wait until the RO water maker’s low-pressure cut-off stops the system. Both ways work, but the latter results in lower freshwater output during the last stages of filter clogging.

By replacing these filters regularly, it's better for the RO water maker and it will make the system last longer.

Qualify of water filters

When changing filters, resist the temptation to use less-expensive pool or spa filters, although 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 slightly more expensive but they last about five times longer than the standard kinds.

Superyacht Windows

Keep your RO water maker clean and tight

By cleaning an RO water maker 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 leaks could occur because of the vibration of the system

Due to the fact that the system is subject to vibrations transferred from the vessel and the equipment, all of the RO water maker 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 be subject to the most vibrations.

Cleaning the salinity probe

It's a good idea to check the salinity probe or salinity metre. 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 without any debris. Use a soft bristle brush if there is any debris built-up on the probes, clean it's thread and then screw it back on clockwise.

If in doubt of the RO water maker salinity probe’s accuracy, pocket salinity metres are available to double check water quality. 

Change the crankcase oil

The high-pressure pump has a little oil reservoir that is very important to check after the first 50 hours and then every 500 hours of usage. Most water maker manuals state when to do an oil change so read your water maker manual to know what the recommended time is.

Changing the crankshaft oil is very straightforward. Get the recommended oil from the RO water maker’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.

Always test after maintenance is complete

It is best to test the RO water maker in open ocean conditions 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 the system 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 to 40 psi after this period of time; gradually increase the system pressure until the system is making its rated water output.

Check the system operating pressure, feed water TDS and system output. If the system comfortably makes its rated product water output, there is no further testing to do on the water maker.

Refit Sky Scraper

A guide on reverse osmosis (RO) water maker maintenance

Reverse osmosis (RO) water maker maintenance
Yachting Pages

Yachting Pages

220 92

Reverse osmosis (RO) water maker maintenance

Written by Michael Henson | With thanks to Hydro Marine

A reverse osmosis (RO) water maker has become an increasingly more important piece of equipment on board a vessel. However like most equipment, marine water makers need maintenance.  RO water makers only require minimal amount of maintenance to keep them in a healthy state and prolong its lifespan.

Below is a list of 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 water maker producing eight to 15 litres of water an hour.

The hull of a superyacht on the water

Water maker maintenance procedure

Keeping it wet

First of all, 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 have to run it once every week as a minimum. A RO water maker doesn't like to sit still.

Some RO water maker systems have an automatic feature called a 'fresh water flush'- cycle. This means that it automatically flushes the desalinator with fresh water. However that only works when the electricity supply to the water maker is continuous.

If, for some reason, the power goes out and then back on, the timer starts from zero, so technically the RO water maker may not have been flushed for weeks, if it is left unattended like that.

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 RO water maker filters

An RO water maker 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, according to the experts, watch the pressure daily and change the filters when it falls below a certain point, while others ignore the gauges and wait until the RO water maker’s low-pressure cut-off stops the system. Both ways work, but the latter results in lower freshwater output during the last stages of filter clogging.

By replacing these filters regularly, it's better for the RO water maker and it will make the system last longer.

Qualify of water filters

When changing filters, resist the temptation to use less-expensive pool or spa filters, although 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 slightly more expensive but they last about five times longer than the standard kinds.

Superyacht Windows

Keep your RO water maker clean and tight

By cleaning an RO water maker 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 leaks could occur because of the vibration of the system

Due to the fact that the system is subject to vibrations transferred from the vessel and the equipment, all of the RO water maker 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 be subject to the most vibrations.

Cleaning the salinity probe

It's a good idea to check the salinity probe or salinity metre. 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 without any debris. Use a soft bristle brush if there is any debris built-up on the probes, clean it's thread and then screw it back on clockwise.

If in doubt of the RO water maker salinity probe’s accuracy, pocket salinity metres are available to double check water quality. 

Change the crankcase oil

The high-pressure pump has a little oil reservoir that is very important to check after the first 50 hours and then every 500 hours of usage. Most water maker manuals state when to do an oil change so read your water maker manual to know what the recommended time is.

Changing the crankshaft oil is very straightforward. Get the recommended oil from the RO water maker’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.

Always test after maintenance is complete

It is best to test the RO water maker in open ocean conditions 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 the system 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 to 40 psi after this period of time; gradually increase the system pressure until the system is making its rated water output.

Check the system operating pressure, feed water TDS and system output. If the system comfortably makes its rated product water output, there is no further testing to do on the water maker.

Refit Sky Scraper