ROS troubleshooting and repair guide

RO Water Filter System Troubleshooting & Repair Guide


Reverse osmosis filter systems provide water of unparalleled purity. However, they are also known to develop common problems, which need to be resolved in order for them to function properly.

With the help of our reverse osmosis troubleshooting & repair guide, you hopefully have the right tool at hand to face and solve just about any issue without the need to consult a plumber and spend any money.

Find our Quick Check Table below, which lists common RO problems as well as causes and solutions associated with them. You can click on the highlighted name in the left column to jump to the according page section.

RO System Repair – Quick Check Table

No or low water flow from faucetFeed water valve closedOpen feed water valve
Water storage tank valve closedOpen water storage tank valve
Feed water pressure below 35-40 psiIncrease pressure in your home or install a pressure pump
Water storage tank over or underpressurizedSet pressure to 6-8 psi when tank is empty (or according to manufacturer specifications)
Membrane clogged/fouledReplace membrane
Filter(s) cloggedReplace filter(s)
Tubing bentStraighten all water lines
Empty storage tankLet storage tank refill and consider buying a pressure pump to increase flow rate
Water running continuously down the drainShut-off valve brokenReplace shut-off valve
Check valve brokenReplace check valve
Feed water pressure below 35-40 psiIncrease pressure in your home or install a pressure pump
System installed improperlyRe-check the whole system
Flow restrictor worn outReplace flow restrictor
Leaking air gap faucetDrain line blockedClear off the drain line
Drain saddle shiftedAlign drain saddle with drain hole
Leaking faucetLoose fittingTighten fitting
Faucet stem leakingReplace faucet
Water tastes or smells unpleasantDepleted filters or membraneReplace depleted components
Fouled membraneReplace membrane
Stagnant waterFlush entire system once or twice
Milky waterNew system or filtersWill subside over time
Noisy drain/air gap faucetNew system or filtersWill subside over time
Tubing bentStraighten all water lines
Filter/membrane housing leakingO-ring displacedCheck if O-ring is worn out and needs replacement
Housing cap looseRetighten the cap
Housing damagedReplace the housing
Fitting LeakingFitting connected improperlyReconnect fitting
Fitting damagedReplace fitting
No water goes down the drainClogged flow restrictorClean or replace flow restrictor

Troubleshooting Reverse Osmosis Systems – Common Problems

Usually, it’s really simple to troubleshoot the most common problems that people find with their RO system.

Slow Water Flow From Faucet

You had your RO system for a number of years, and like every other morning you want to fill a glass of water, but all of a sudden the glass only fills half full and the water flow goes down to a trickle.

Little or no flow coming from the faucet means that you either have low volume of water or low pressure.

The problem is likely caused by a malfunctioning storage tank. Inside the tank is an air bladder that, as more water flows into the tank, increases pressure. If the bladder leaks or breaks, it cannot build up enough pressure, so you are not going to get water delivered to the faucet in the amount you are accustomed to.

To solve the problem, lift the tank to check if it’s full. A full tank weighs somewhere around 20 lbs as opposed to an empty one, which ways around 1-2 lbs. If the tank feels full and heavy, the problem is probably inside of it.

Pressurize RO Tank

Here is what you need to do:

  1. Shut off the cold water supply to the system.
  2. Close the storage tank valve.
  3. Disconnect the tank from the system and take it outside, so you can open the tank valve to drain out the water inside of it. In the beginning, the water will pour out, but after some time the flow will decrease to a trickle.
  4. As a lot of water is still inside the tank, you have to pump air into the tank’s pressure vessel using a bicycle pump or a compressor. With each pump, more water will pour out.
  5. Once the tank is empty, take a pressure gauge to measure the pressure inside of it. It should read about 6-8 psi. If your tank’s pressure is below, you need to carefully re-pressurize it, again using a pump or compressor.
  6. When you are done, reconnect the tank to you RO system and open up the tank valve and the feed water valve, and let the system refill.

If the problem reoccurs a couple of days later, this means that the bladder inside the tank isn’t holding the pressure. In that case, you need to replace the whole tank.

slow water flow from faucet

Slow faucet water flow can also be an indicator for overall low feed water pressure (below 40 psi). A booster pump is your best option then. And there are a couple of other reasons that can cause the issue:

  • Clogged filters/RO membrane – Membrane clogging usually occurs when a membrane has to process exceptionally hard water. You have two options here: You can either replace your system’s RO membrane more frequently, which will add up to the maintenance costs, or you can additionally install a water softener in your home, which removes the hardness minerals from the water before it enters the filter system. If clogged filters are causing the low water flow, you need to replace them, too. This is especially true, if you have installed your RO system in a new home with temporary higher levels of debris and sediment in the plumbing system.
  • Bent tubing – Bent tubing also results in the reduction of pressure which in turn causes low water flow. You should check the tubing and straighten all water lines that are bent.

Water Running Continuously Down the Drain

Each RO system works on pressure. When the storage tank is full and has full pressure, it triggers the automatic shut-off valve to close down, which stops more water flowing into the system. It also stops more rejected water flowing down the drain line.

If the shut-off valve doesn’t close properly or not at all, or the check valve is broken, water continuously runs down the drain line. This means that your reverse osmosis system is not only wasting a lot of water, it also makes noises, which can become quite annoying after a while.

The solution: Measure the pressure in the storage tank with a pressure gauge when the tank is full. You know if your tank is full by trying to lift it up. The pressure in the tank needs to be 35-40 psi. If it is, then either your shut-off valve or check valve is most likely defect and needs replacement.

Checking Valves: Test #1

valve test 1

Here is how you can test if both your automatic shut-off valve and check valve are functioning properly:

  1. Draw about 20 oz. of water from the faucet to drop the pressure in the tank so your RO system will start processing some water to refill it.
  2. Close the tank valve to mimic a full tank.
  3. Wait for 5 minutes.
  4. Check if water stops flowing down the drain line by either listening closely or pulling the drain line out of the drain saddle. If so, both valves are working as intended. If, however, water does continue to flow down the drain line, either the automatic shut-off valve or the check valve is broken. In that case, continue with test #2.

Checking Valves: Test #2

valve test 2

  1. Let the tank refill and keep the tank valve open.
  2. Turn off the feed water valve.
  3. Check if water is still flowing down the drain line by either listening closely or pulling the drain line out of the drain saddle. If so, the water is coming out of the storage tank meaning that the check valve is broken and needs replacement. If no water is flowing, the system’s automatic shut-off valve is broken and needs to be replaced.

Other causes for water running continuously down the drain line of your RO system are:

  • Feed water pressure is below 40 psi. If that’s the case, increase the pressure to the required level by applying a pressure pump.
  • Your system wasn’t properly installed and it’s likely that the membrane causes the overflow. Therefore, take great care to fit all system parts in their correct positions. If you need help with your RO system installation, click here.
  • If the flow restrictor inside the drain line is worn out, it might cause the system to never stop running. Replace the restrictor.

Reverse Osmosis Air Gap Faucet Leaking

Is there water coming out of the hole of your air gap faucet above the sink? Then you are experiencing a very common issue called an ‘air gap leak’ that occurs when your drain line is blocked, which usually happens when debris, e.g. from food, accumulates in the drain.

The purpose of an air gap is to assure that drain water cannot flow backwards into your RO filter system. In normal operation water runs from the storage tank up to the faucet and falls through a small pocket of air called an ‘air gap’. When the drain line starts clogging up, it creates back pressure, which causes water to flow out of the faucet and all over your sink.

All you have to do to fix the issue is clear off the drain line, so water is able to flow freely again. Take a pipe cleaner or wire brush to clean out the end of the drain line that is connected to the drain saddle, and also clean the drain saddle itself, because stuff tends to grow in there. Drain saddles also tend to shift so the holes aren’t lined up anymore, which also restricts the water flow. So make sure to align the drain saddle with the drain line hole.

How Can You Prevent an Air Gap Leak?

Completely eliminating the chance for an occasional air gap leak is almost impossible, however, you can take the necessary precautions that reduce the frequency in which an air gap occurs significantly.

  • First of all, avoid rinsing large chunks of food or other stuff down the drain line.
  • Regularly treat your drain line with natural cleaner to dissolve possible blockades.

No Matter How Hard You Try, Sometimes You Have to Admit that Something Is Broken Beyond Repair. If You Need a Replacement, Find the Best RO Systems Here.

Dripping or Leaking Faucet

A dripping faucet indicates that one or more system parts are loosely fitted. To stop the leaking, thoroughly tighten all fittings. Push the tubing further into their ports, valves, and drain saddle. If the leaking originates from the bottom of the faucet stem, there is no way around replacing the piece.

Bad Taste and Odors

Nothing is more deterrent than water that tastes and smells unpleasant. And it might sound like a bad joke, but a handful of customers have reported that their supposedly high-quality water purification systems added a strange taste and/or odor to their drinking water instead of removing them. The only way you can prevent this from happening is to invest your money in a decent system that is up to today’s standards.

It’s also possible that after months or years of using your RO system, the filtered water starts to turn cloudy. This is usually caused by biofilm accumulation in the system’s filter stages. Therefore, what you should do is replace any clogged filters or fouled membrane(s) immediately, and from there on replace these components on a more regular basis (every 6-12 months). Remember: If you let germs accumulate in your RO system, it can pose a serious threat to your health.

Investing in an RO system that allows you to dispose the filter together with the filter housing has proven to be the best way of preventing the accumulation of germs not only in your filter unit, but also in the water that flows through it. These kinds of systems are usually more expensive and filter replacements are also more costly.

In general, we recommend you to maintain your RO system periodically and to clean it according to the manufacturer’s instructions. This also includes sanitizing the storage tank.

Unused Water

Over time bacteria starts to grow in stagnant water, which can be the source of bad taste and smell. If you haven’t used your RO system for a while, it’s a good idea to flush the entire system (and the storage tank in particular) once or twice before you restart using the water.

old clock

Noisy Air Gap Faucet or Drain

When you put your RO system into use for the first time, or just recently you’ve replaced one or more of the filter cartridges, the drain line may make some noises, which is nothing to worry about. It’s caused by air being pushed out of the system. However, the issue is not supposed to persist for more than a couple of days or weeks at maximum.

If the noise doesn’t subside and it bothers you, make sure that all tubing is set straight. The noise can also be caused by a restriction in the drain tube or drain saddle. So make sure that the problem doesn’t originate from there.

If that doesn’t help, it’s time to check the entire system for gaps and correct any detected faults.

Leaking Filter or Membrane Housing

A worn-out rubber O-ring might be causing a leak in one of your system’s filter housings. Follow these instructions to solve the issue:

  1. Close the feed water valve so no more water can flow into the system.
  2. Close the storage tank valve.
  3. Unscrew the leaking filter housing.
  4. Replace the O-ring if it looks worn out.
  5. Also make sure that the O-ring is placed correctly.
  6. Screw the filter housing back onto the system module and hand tighten it. Next use a housing wrench to carefully tighten the housing a bit more.
  7. Open up the tank and feed water valves.
  8. Check for leaks. If the filter housing is still leaking, it may be damaged and needs replacement. You can check if the housing is causing the problem by exchanging it with one of the system’s other filter housings.

It’s also quite common for a housing cap to come loose over time, which displaces the O-ring. Therefore you should periodically re-tighten it.

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If you have any questions or thoughts about how to troubleshoot and repair an RO system, please don’t hesitate to leave a comment below!

Leave a Comment:

Rekha Goel says a few months ago

From August 27th to September 3rd – the water tasted bitter and caused a sick feeling after I drank. Now today it is ok. Could there be something temporary that caused water to taste bitter for a few days?

    Gene says a few months ago

    Absolutely! Although it’s impossible for us to tell what caused the temporary issue and if/when it might reoccur.

Kelly says a few months ago

My water that comes from the facet that the RO is Constantly running so I had it shut it off can you give me any hints please

    Gene says a few months ago

    If an RO system is constantly running, this usually has to do with a broken stut-off valve. If you mean that your faucet is constantly running, I guess the faucet doesn’t close properly and needs replacement.

Brian says a couple of months ago

Replacing my filter for the first time. There was a motiveless leak from the collet on the new filter. I took the filter off & put the old one back & now that one is leaking as well. Any thoughts?

    Gene says a couple of months ago

    Hi Brian,
    Thanks for the question. Is this a filter with a housing? In this case, the O-ring might be misplaced or worn out.

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