Under Sink Reverse Osmosis System Maintenance Guide

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An under sink reverse osmosis system effectively purifies water for drinking, cooking, and other household uses.

But unless properly maintained, it can become clogged with dirt and mineral buildup, reducing its effectiveness and leading to costly repairs or replacements.

With a few simple steps, you can ensure that your under sink RO system continues to work optimally, giving you access to pure water whenever needed.

Key Takeaways

  • Following the filter change schedule is the most critical factor in under sink reverse osmosis system maintenance. Pre-filters should be changed every 6-12 months, post-filters every 12-24 months, and the RO membrane every few years.
  • Cleaning and sanitizing an RO system should ideally be done once a year.
  • Keep an eye out for leaks and wear and tear that indicate the need for the O-rings to be changed.
  • If you forget to follow the maintenance schedule, stop drinking the RO water immediately until you have sanitized the entire system and replaced all the filtration components.

How to Maintain an Under Sink Reverse Osmosis System

So, how do you maintain an under sink reverse osmosis system?

The absolute most crucial thing when maintaining under sink RO filtration systems is to change the filters regularly – no surprise.

The condition of the source water will influence how often the filters need changing. For example, if you have feed water with a lot of sediment, or hard water, it can reduce the lifespan of your pre-filters by quite a lot.

The other thing to consider is how often the RO system is used. If you are using it just for one person’s drinking water, the filters will last longer than for drinking and cooking for an entire family.

Under Sink Reverse Osmosis System

Generally speaking, pre-filters need replacing every 6-12 months, while a post-filter could last a couple of years.

The RO membrane can last up to 3-5 years, provided you kept any pre-filters in good condition.

Not keeping up with the maintenance schedule for filter change can result in pathogens being active in your drinking water, a drop in your water pressure, higher wastewater production, and possibly changes to the aesthetics of your water.

Maintenance Schedule

Biannual Tasks Annual Tasks Every 3 to 5 Years
Replacing pre-filters Replacing pre-filters
Replacing post-filter(s)
Replacing RO membrane
System cleaning/sanitizing
Checking storage tank pressure

How to Replace Under Sink RO Filter Elements

Your product manual would contain specific step-by-step instructions for your particular system. The following is a general process that works for most under sink RO models, but remember that they all are slightly different.

  1. Turn off the water supply to RO system and the storage tank valve.
  2. Depressurize the unit by opening the faucet.
  3. Remove filters or the membrane (whatever needs replacing) from their housings.
  4. Insert the new elements and screw the housings back on.
  5. Turn on the water supply and open the tank valve.
  6. Open the RO faucet and let the system flush for a few minutes.
  7. Check for leaks while the system is flushing.
  8. Close the faucet to let the tank refill (this can take 3 to 10 hours).
  9. Discard 1 or 2 full tanks of water before use to eliminate any tastes or smells from the new filters.

How Often to Replace

  • Pre-filters should be replaced every 6-12 months
  • The RO membrane should be replaced every 3 to 5 years.
  • Post-filters should be replaced every 12 months.

Sediment Pre-Filter

This is the first stage filter in your RO system. It removes the bigger bits of sediment so that your RO membrane can focus on filtering out the microscopic contaminants. It also prevents the RO membrane from clogging or fouling.

The sediment pre-filter needs to be changed every 6 to 12 months.

Carbon Pre-Filter

Stage 2 or 3 of your under sink reverse osmosis system will be the carbon pre-filters. Among other contaminants, this removes any chlorine and some other water disinfectants. Chlorine is very damaging to the delicate RO membrane and needs to be removed from the water before it passes through the RO filtration step.

These block or granular carbon pre-filters should be changed every 6 to 12 months.

Reverse Osmosis Membrane

At the heart of the operation, the RO membrane filters out up to 99.9% of all the other contaminants from your water, leaving almost 100% pure H2O. RO membranes have a longer lifespan than the filters, but only if you replace the pre-filters according to schedule. The best way to determine if your RO membrane is no longer working as it should, is to test for total dissolved solids in the RO water.

Check the manual or with your manufacturer to know exactly when your RO membrane should be replaced.

Carbon Post-Filter

Carbon post-filters remove any residual tastes and odors that may have come from the water sitting in its storage tank. They should be changed every 12 months, but some can last up to 2 years.

Different Water Filter Cartridges and Membranes

How to Clean/Sanitize Your Under Sink RO System

Sanitizing your RO system may be necessary in some cases, such as after a boil water advisory, or if you have not adhered to the filter maintenance schedule. We recommend cleaning it at least yearly just to be on the safe side. To clean and sanitize your system:

  1. Turn off the water supplying the RO unit.
  2. Run the faucet to depressurize the system.
  3. Remove all filters + membranes from their housings.
  4. Scrub the inside of the housings with warm water and dish soap, then rinse.
  5. Add unscented household bleach or the manufacturer-recommended sanitizing solution into the housing of filter stage one.
  6. Screw all housings back on (not the filter cartridges)
  7. Turn on the water supply, then open the RO faucet until water comes out. Then close it.
  8. Check for leaks.
  9. Let the storage tank fill and sit for at least 30 minutes. This will allow the bleach to stay in the system and disinfect it.
  10. Flush out all water.
  11. Let the tank refill again, and flush it all out again.
  12. Turn off the water supply and depressurize the system once again.
  13. Install the new RO membrane and other filter elements.
  14. Turn the water supply back on.
  15. Open the RO faucet and let the system flush for a few minutes.
  16. Close the faucet to let the tank fill (could take 3-10 hours).
  17. Discard 1 or 2 full tanks of water before use (check the manufacturers’ instructions).

Some RO membranes can also be soaked in a chemical solution. Refer to the manufacturer to see what is recommended for yours.

Maintaining Storage Tank Pressure

If you don’t have adequate pressure in your RO storage tank, not only is there a possibility of increased wastewater, but you won’t have a sufficient flow rate from your faucet. A pressure gauge will do the trick to check it. When the tank is empty, it should measure at 6-8 psi. If it is less, you can use a bicycle pump to increase it.

  1. Shut off the water supply to the RO system.
  2. Close the storage tank valve, disconnect the tank, and take it outside.
  3. Open the tank valve and let the water out.
  4. Pump air into the pressure valve with a bicycle pump or compressor to get more of the water out.
  5. When the tank is empty, take the pressure gauge to measure the pressure inside. You should aim for somewhere between 6 to 8 psi for most tanks.
  6. Carefully repressurize if need to by using the pump or compressor.
  7. Reconnect the tank to your under sink reverse osmosis system.

Signs Your Under Sink RO Filter Is Due for Maintenance

While a lot of the time, there may be no sign that the RO system needs maintenance, as many water contaminants leave no taste or smell, there are some things to look out for:

Unpleasant Water Taste or Odor

RO water should have almost no taste and no smell. If your water has an unpleasant taste or smell, it is a sign that one or more of the filters may need replacing.

young woman drinking water

Low Water Pressure

Storage tanks may need to be repressurized.

System Is Running Constantly

The storage tank is not triggering that it is full, and it may need to be repressurized, or you may need a new storage tank. A broken valve may also be causing the issue.

Why Is RO System Maintenance Important?

RO system maintenance is essential mainly because there may be no sign that your water is contaminated. For one, most viruses and bacteria are invisible to the naked eye and have no taste or smell, so you wouldn’t know if you were drinking something potentially harmful. Staying on track with the maintenance schedule ensures the system is always effectively filtering contaminants from the water.

Another factor is wastewater. An improperly maintained under sink RO unit could waste considerably more water than a system that’s in shape.

I Forgot to Change Filters. What Now?

If you have forgotten to change the filters, you will need to stop drinking the water, remove and discard the old filters and the RO membrane, flush and sanitize the entire system, and then replace the filtration components with new ones.

You may even consider purchasing a new storage tank, as it cannot be opened to clean inside and may be contaminated.

Additional Tips to Help Maintain Your Under Sink Reverse Osmosis System

  • Always keep an eye out for leaks when you are using the device. This is a sign that your O-rings need to be replaced.
  • Write down your maintenance schedule in your planner, and set reminders on your phone.

If you have any questions about under sink reverse osmosis system maintenance please don’t hesitate to leave a comment below!

About the Author Gene Fitzgerald

Gene Fitzgerald is one of the founders of BOS and currently head of content creation. She has 8+ years of experience as a water treatment specialist under her belt making her our senior scientist. Outside of BOS, Gene loves reading books on philosophy & social issues, making music, and hiking.
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