How to Troubleshoot All Common Reverse Osmosis System Problems

This page may contain affiliate links. If you buy a product or service through such a link we earn a commission at no extra cost to you. Learn more.

Reverse osmosis systems usually last for years without causing trouble.

But even if yours doesn’t, the good news is that most problems are really simple to diagnose and repair, especially with the help of our RO Troubleshooting Guide below.

With it you hopefully have the right tool at hand to face and solve just about any issue without the need to call a professional and spend any money.

RO Troubleshooting & Repair Guide – Overview of Common Problems

The following table lists common RO system problems + potential causes and their solutions. Click on the highlighted names in the left column to jump to according page sections.

(Mobile Hint: Swipe to Scroll)

Problems Possible Causes Solutions
RO system drains constantly (drain line keeps running) Storage tank pressure too low Measure + repressurize
Damaged tank air bladder Replace tank
Broken shut-off valve Test + replace
Broken check valve Test + replace
Feed water pressure below 40 psi Increase pressure in your home or install a booster/permeate pump
System installed improperly Re-check the whole system
Reverse osmosis membrane in bad condition Replace
Worn-out flow restrictor Replace
RO storage tank not filling up Storage tank pressure too high Measure + release pressure
Feed water pressure below 40 psi Increase pressure in your home or install a booster/permeate pump
Reverse osmosis membrane in bad condition Replace
Clogged filter(s) Replace
RO membrane not properly seated Readjust
Bent tubing Straighten all water lines
Feed water valve closed Open valve
Water storage tank valve closed Open tank valve
Leaking system Loose connection Tighten
Damaged connection Replace
Leaky faucet Loose connection Tighten
Damaged faucet stem Replace faucet
Clogged drain line (air gap faucets only) Unclog
Shifted drain saddle (air gap faucets only) Realign drain saddle with drain hole
Leaking filter/membrane housing Misplaced O-ring Reposition
Worn-out O-ring Replace
Loose housing cap Retighten
Damaged housing Replace
Slow/no water flow from faucet & low pressure Storage tank pressure too low Measure + repressurize
Damaged tank air bladder Replace tank
Storage tank pressure too high Measure + release pressure
Feed water pressure below 40 psi Increase pressure in your home or install a booster/permeate pump
Reverse osmosis membrane in bad condition Replace
Clogged filter(s) Replace
RO membrane not properly seated Readjust
Clogged flow restrictor Unclog or replace
Bent tubing Straighten all water lines
Empty storage tank Let storage tank refill and consider buying a pressure pump to increase flow rate
Feed water valve closed Open valve
Water storage tank valve closed Open tank valve
RO water tastes bad Depleted filters or membrane Replace + clean system periodically
Fouled membrane Replace + clean system periodically
Stagnant water Flush entire system once or twice
Noisy air gap faucet or drain New system or recent filter replacement Will subside over time
Bent tubing Straighten all water lines
Restriction in drain saddle or tubing Unblock
Connection with air gap Check system and tighten loose connections
Cloudy water Trapped air in newly installed system or filters Will subside over time
No water goes down the drain Clogged flow restrictor Clean or replace
Clogged drain line Unclog
Low permeate and drain flow rates Clogged pre-filters Replace
Low permeate flow rate Clogged RO membrane Replace
Low permeate flow rate and high drain flow rate Failed flow restrictor Replace

RO System Drains Constantly (Drain Line Keeps Running)

The functioning of a reverse osmosis system is based on pressure. Simply put: Feed water flows into the unit, gets purified and is then stored in the storage tank for later use. When the storage tank is full it triggers an automatic shut-off (ASO) valve to close. The valve stops more water from entering the system. A second valve, the check valve, prevents reject water from running down the drain line.

If tank pressure is too low or the shut-off valve or check valve is broken, water might flow continuously down the drain. This means that your RO system not only wastes a lot of water, the noise can also become quite annoying after a while.

How to fix a reverse osmosis that constantly drains?

First, use a pressure gauge to measure the pressure in the storage tank when empty. The tank should read about 6-8 psi. In case the pressure is too low you need to repressurize.

plumber installing reverse osmosis system under sink

How to Drain & Repressurize an RO Tank

  1. Shut off the water supply to the system.
  2. Close the storage tank valve.
  3. Disconnect the tank from the system and take it outside. Open the tank valve. In the beginning, water will pour out quickly, but after some time the flow will decrease to a trickle.
  4. Since a lot of water is still inside the tank, you have to pump air into the pressure valve with the help of a bicycle pump or compressor. With each pump more water will pour out.
  5. Once the tank is empty, take a pressure gauge to measure the pressure inside. For most tanks you should aim for somewhere between 6 to 8 psi (optimal value might state on tank label). Very carefully repressurize if need be using the pump or compressor.
  6. Now you can reconnect the tank to your reverse osmosis system. Open the tank and feed water valve and allow the system to refill.

The problem reoccurred a couple of days later? This means that the bladder inside the tank is ruptured and cannot hold the air. All you can do is replace the whole tank.

Tank pressure is within the desired range? Then it’s likely that either the shut-off valve or the check valve is defect and needs to be replaced…

Checking Valves

Here is how you can test if both ASO and check valve are functioning correctly:

Test #1

  1. Let the storage tank fill completely. You know when the tank is full by trying to lift it up.
  2. Draw 2 to 3 glasses of water from the RO faucet to reduce the pressure inside the storage tank. This will cause your system to start processing more water to refill.
  3. Close the tank valve to mimic a full tank.
  4. Wait for 5 minutes.
  5. Check if water stops flowing down the drain line by either listening closely or by pulling the drain line out of the drain saddle. If so, both valves are working just fine. If, however, water does continue to flow down the drain, either the automatic shut-off valve or the check valve is broken. In that case continue with test #2.

Test #2

  1. Let the tank refill.
  2. This time keep the tank valve open and turn off the feed water valve.
  3. Check if water is flowing down the drain by either listening closely or by pulling the drain line out of the drain saddle. If so, the water is coming straight out of the storage tank which means that the check valve is broken and needs replacement. If no water is flowing the ASO valve is broken and has to be replaced.

Other Possible Causes

Other possible causes for a system to constantly drain are:

  • Feed water pressure is too low (usually below 40 psi). Increase the water pressure to the required level, e.g. by applying a booster pump.
  • Your system wasn’t installed properly so that the membrane causes the problem. Carefully reconnect all pieces making sure that they are in their correct position. Need help with how to install a reverse osmosis system?
  • The RO membrane is in bad condition. Replace it.
  • A worn-out flow restrictor inside the drain line is causing the problem. Replace the restrictor.

No matter how hard you try, sometimes a unit is broken beyond repair. If you need a replacement, you can find reviews of the best RO systems here.

RO Storage Tank Not Filling Up

If a storage tank does not fill there is usually an underlying pressure issue. Either tank pressure is too high or feed water pressure too low.

An empty storage tank should read roughly 6 to 8 psi. You can measure this with a standard bicycle gauge for example. Reduce pressure if need be.

If the feed water pressure is less than 40 psi you need to either increase the pressure in your entire home or use a pump specifically designed for reverse osmosis systems.

That wasn’t it? Also consider:

  • Clogged filters or bad RO membrane – Clogging usually occurs when a membrane has to process exceptionally hard water. You have two options: You can either replace membranes more frequently which will add to the costs. Or you can install an additional pre-treatment system – think water softener – which will remove all hardness minerals from the water before it enters the filter system. If one or more clogged filters are causing the problem, again, replacement is necessary.
  • RO Membrane not properly seated
  • Bent tubing
  • Feed water valve or tank valve closed

Different Water Filter Cartridges and Membranes

Leaking System

Most of the times it’s easy to identify what’s causing a reverse osmosis system to leak. Simply check every single connection in order to find the culprit.

Leaky Faucet

A dripping faucet indicates that one or more system parts are loosely fitted. To stop the leaking, thoroughly tighten all connections. Push the tubing further into their ports, valves and the drain saddle.

If the leaking originates from the bottom of the faucet stem there is no way around replacing the piece.

Leaking Air Gap Faucet

Water is coming out of the hole of the air gap faucet above the sink? This commonly known issue is called an “air gap leak“. It’s the result of a blocked drain line which usually happens when debris has accumulated in the drain.

Now, the purpose of an air gap is to assure that water cannot flow backwards into the RO unit. During normal operation, water runs from the storage tank to the faucet and falls through a small pocket of air, the air gap.

When the drain line starts to clog up it creates backpressure which causes water to flow out of the gap and all over your countertop.

All you have to do to fix this is to clear off the drain line so water can flow freely. Take a pipe cleaner or wire brush to clean out the one end of the drain line that is connected to the drain saddle. Also clean the saddle itself, as stuff tends to grow in there.

What’s more, drain saddles tend to shift so the holes aren’t properly lined up anymore, which may also restrict the water flow. Make sure that drain saddle and drain line hole are aligned.

How to prevent an air gap leak in future?

Completely eliminating the chance of an occasional leak is almost impossible. However, you can take the necessary precautions to reduce their frequency quite significantly:

  • First of all, avoid flushing large chunks of food and other stuff down the drain.
  • Furthermore, regularly treat your drain line with natural cleaner to dissolve any blockades.

Leaking Filter/Membrane Housing

A misplaced or worn-out rubber O-ring is most likely responsible for causing a filter/membrane housing to leak. Here is what you should do:

  1. Close the feed valve so no more water can flow into the system.
  2. Close the storage tank valve.
  3. Unscrew the leaking filter housing.
  4. Inspect the O-ring(s). Replace if cracked or generally in a bad condition.
  5. Make sure that O-rings are placed correctly and sit tight.
  6. Screw the filter housing back on and hand tighten. Use the housing wrench to tighten an additional quarter turn or so.
  7. Open up the tank and feed water valve.
  8. If the filter housing is still leaking it may be damaged and needs replacement. You can check for this by switching it with one of the other housings.

It’s also quite common for the membrane housing cap to come loose over time which displaces the O-ring. Periodical retightening is an easy fix.

Slow/No Water Flow From Faucet & Low Pressure

You had your reverse osmosis system for a number of years and like every other morning you are about to enjoy a refreshing glass of purified drinking water. For some reason, however, the glass only fills half full and the water flow goes down to a trickle.

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

The root of the problem is most likely a malfunctioning storage tank. Inside the tank is an air bladder that, as more water runs into the tank, increases pressure. If the bladder leaks it cannot build up enough force. As a result, you are not getting water delivered to your faucet in the same amount you are used to.

What can you do about this?

First, lift the tank to see if it’s full. A full tank weighs somewhere around 28 lbs as opposed to an empty one weighing almost nothing. If the tank feels heavy the defect is probably in its inside.

Next, you want to measure the pressure of the tank when empty. An empty tank should read somewhere between 6 to 8 psi. If the pressure in your tank is lower then you need to repressurize it (learn more above).

The problem reoccurred a couple of days later? This means that the bladder inside the tank is ruptured and you need to replace the whole tank.

young girl opening reverse osmosis faucet

Other Possible Causes

Slow faucet water flow can also be an indicator for overall low feed water pressure (below 40 psi). A booster or permeate pump is your best option here. Other reasons that could be causing the issue are:

  • Clogged filters or bad RO membrane – Clogging usually occurs when a membrane has to process exceptionally hard water. You have two options: You can either replace membranes more frequently which will add to the costs. Or you can install an additional pre-treatment system – think water softener – which will remove all hardness minerals from the water before it enters the filter system. If one or more clogged filters are causing the drop in flow, again, replacement is necessary.
  • RO Membrane not properly seated
  • Clogged flow restrictor
  • Bent tubing – Bent tubing may result in pressure loss which in turn causes low water flow. Check the tubing and straighten all lines that are bent.
  • Empty storage tank
  • Feed water valve or tank valve closed

RO Water Tastes Bad

Bad water taste and/or odor usually originates from a biofilm that has accumulated in one or more of the filtration stages. This can happen after months or years of use and might also lead to cloudiness.

Therefore, what you should do is replace any clogged filters or a fouled membrane immediately. And from now on keep in mind to replace said components in a more timely manner (filters at least every 6 to 12 months).

Remember: If you let germs grow in your reverse osmosis system they can pose a serious health threat.

In addition, we recommend you clean the RO system periodically (refer to manufacturer instructions). This may also include sanitizing the storage tank.

Alternatively, you can invest in a unit that features a modular filter design. This allows you to dispose of the entire filter/membrane housings with every replacement which has proven to be the best way to prevent the accumulation of harmful pathogens. The downside is that this type of system is more costly to purchase and to maintain.

Unused Water

Bacteria grows in stagnant water over time, 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 unit, the storage tank in particular, once or twice before you start using the water.

Noisy Air Gap Faucet or Drain

When you put your system into use for the first time or you just recently replaced one of the filter cartridges, you might hear strange noise coming from the drain line or air gap faucet.

This is nothing to worry about. It’s caused by air being pushed out of the system.

However, the issue should not persist for more than a couple of days. If the noise doesn’t subside and it’s something that is bothering you, make sure that all tubing is set straight. The noise can also be caused by a restriction in the drain tube or saddle. If that doesn’t help, it’s time to check the entire system for gaps and correct any errors.

Problems with Permeate and Drain Flow Rate

Permeate flow rate refers to the rate of water passing through the RO membrane.

To determine if you have a problem with your permeate flow rate, you’ll need to perform a little testing and calculation. You’ll need to establish both the permeate flow rate and the drain flow rate, and then compare them to the ideal numbers to get an idea of what is going on.

To find the permeate flow rate:

First up, you’ll need to shut off the tank valve and open the RO faucet. This will send the water directly from the RO membrane to the faucet. Wait until the water is flowing consistently, and then collect 60 seconds’ worth of water flow in a measuring cup.

Related to the permeate flow rate is the drain flow rate, which refers to the rate of flow through the drain line and out the drain saddle.

Reverse osmosis systems require flow restriction at the drain line to keep the pressure high enough for the RO membrane to work correctly. This is the job of the flow restrictor.

To find the drain flow rate:

First, disconnect the drain line from the drain saddle, and then position the line inside a measuring cup. Run the faucet for another 60 seconds and take note of the water quantity collected.

Now that you have both of these flow rate figures, it’s time to compare them to the chart below:

Membrane GPD Rating Permeate Flow Rate Drain Flow Rate
25 Gallons Per Day ~2 Ounces Per Minute ~9 Ounces Per Minute
50 Gallons Per Day ~4 Ounces Per Minute ~12 Ounces Per Minute
75 Gallons Per Day ~6 Ounces Per Minute ~20 Ounces Per Minute
100 Gallons Per Day ~9 Ounces Per Minute 25-30 Ounces Per Minute
  • If both results are in the optimal range, then your system is working as intended and there’s no need to do any more troubleshooting.
  • If both results are lower than the optimal range, then remove the pre-filters from their housings and re-run the test. If the results stay the same, it’s likely that you have a low-pressure issue, and may need to install a pressure regulator.
  • If the drain flow rate is within the acceptable range, but the permeate flow rate is very low, then this is an indication that you have an issue with your RO membrane. The membrane may be calcified or clogged and is no longer functioning properly. You’ll likely need to replace the RO membrane, and you may need to install additional pre-filters to reduce the level of TDS (total dissolved solids) in your water.
  • If the drain flow rate is high, but the permeate flow rate is very low, this indicates a problem with your flow restrictor. If the flow restrictor has failed or is not working properly the system won’t have the necessary pressure for the RO membrane to work properly. In this case, you’ll likely need to replace the flow restrictor.

Components of a Reverse Osmosis Filter System

Reverse osmosis systems are relatively complex systems, utilizing multiple pre and post-filters in addition to the primary RO membrane among other components. Let’s take a look:

Under Sink Reverse Osmosis System

  • Feed water valve: The feed water valve is the connection between your sink’s cold water supply and the RO system’s first pre-filter.
  • Pre-filter(s): The pre-filter or pre-filters are the filtration stages before feed water reaches the RO membrane. Typically, there will be a sediment pre-filter to remove silt and sand, and a carbon pre-filter to remove chlorine/chloramine, both of which can prematurely age the membrane.
  • RO membrane: The RO membrane is the primary filtration stage, and removes a wide array of contaminant particles down to .0001 microns in size.
  • Storage tank: Because RO systems filter slowly, a storage tank is needed to keep a usable amount of filtered water on hand at all times. Water passes from the RO membrane to the storage tank before it passes through the final post-filter.
  • Post-filter: A final post-filter is used after the water has passed through all of the other filtration stages. This stage is intended to ‘polish’ the taste and remove any residual contaminants left in the water.
  • Check valve: The check valve blocks the water flow backward towards the RO membrane. This prevents potential membrane damage.
  • Flow restrictor: A flow restrictor restricts the flow of wastewater from the RO membrane housing outlet. This is needed to maintain adequate water pressure in the system.
  • Drain line: The drain line transports the contaminant-filled wastewater from the RO membrane to the drain saddle on your sink’s drain pipe.
  • RO faucet: This is simply the faucet that dispenses filtered water at your kitchen sink. It’s separate from your main faucet, so you can still use unfiltered water for cleaning tasks.

If you have any questions or thoughts about reverse osmosis troubleshooting 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.
Learn more about .


Information provided on BOS is for educational purposes only. The products and services we review may not be right for your individual circumstances.
We adhere to strict editorial guidelines. Rest assured, the opinions expressed have not been provided, reviewed, or otherwise endorsed by our partners – they are unbiased, independent, and the author’s alone. Our licensed experts fact-check all content for accuracy. It is accurate as of the date posted and to the best of our knowledge.

Leave a Comment:

Rekha Goel says September 4, 2018

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 September 4, 2018

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

Kelly says October 16, 2018

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 October 17, 2018

    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 October 30, 2018

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 October 31, 2018

    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.

kevin says February 6, 2019

slow water flow. changed membrane, did not fix it. changed flow restrictor and auto shut off. will only flow to tank or flow to drain . switched all possible lines either one or the other

    Gene says February 6, 2019

    Maybe the tank is the real issue and not pressurized properly or the bladder inside is worn out.

Laura Currey-Tack says April 1, 2019

My older RO GE (3 cartridges) system has always worked great but recently I changed the main cartridge out and replaced worn out air gap faucet with the exact same faucet. Whenever I pull out water that is more than a glass or fill coffee carafe the system starts to run and makes gurgling sounds for about two hours, a very annoying noise. Help!!!

    Gene says April 2, 2019

    So the system makes noises when refilling the tank. Did you check the tubing for bends? Also, check for restrictions in the drain line/saddle. It might also be that there is an air gap – check each component.

Carl Maas says April 5, 2019

How soft should RO water be?

    Gene says April 6, 2019

    It really depends on the condition of your feed water.

Cameron says April 8, 2019

How heavy is a proper working storage tank suppose to weigh with water in it? You mention if it is heavy it could be a bad bladder, but what is heavy?

    Gene says April 9, 2019

    It depends on the tank size. A 4-gallon storage tank can hold about 3.2 gallons of water. The rest is the air bladder. 3.2 gallons, that is roughly 26 lbs alone. Plus the tank itself which is not really heavy. So about 28 lbs, maybe a bit more.

Cameron says August 22, 2019

I did the tests for the check valve and shut-off valve all worked right, but after the system was up and running I left the drain line in a bucket, to see how much water was going to the drain. Wow was I surprised, for a 4 gallon tank there was at least 10-gallons that went to the buckets, then it shut off. Is this a normal amount of waste water from the system?

    Gene says August 23, 2019

    It is indeed. Of course, how much goes down the drain line also depends on your system, your incoming water pressure, etc. But the only thing you can really do about this is add a pressure pump. This will lower the permeate:wastewater ratio to something like 1:1. Hope that helps!

      dave says April 7, 2021

      Changing the type of membrane is the best way to save water with your to system,one with a one to one ratio

K says September 6, 2019

Just wanted to say thanks. Our RO system was continuously running. I used your trouble shooting guide to move past our check valve and ASO (which were fine) and repressurized our tank. That was the issue and now the water shuts off appropriately. I did not previously know the tank pressure affected this. Thanks much.

    Gene says September 6, 2019

    Hey K,
    That’s great news. Always happy to help. Thanks for letting us know!

Colin James says September 14, 2019

I’ve just brought a new ro unit with new membranes filters and resin.
Set it all up. I didn’t realise that for 2 days I’ve had the blue tap on flush!!!
Have I damaged the membranes and filters in doing this???
Please get back to me, thank you.

    Gene says September 20, 2019

    Hey Colin,
    What is the “blue tap” you are referring to? What model are you using?

Donna Zacharczyk says September 21, 2019

I had to have the water shut off to the house and while it was off I did use water from the tank. When the water was turned back on, the tank must not have refilled because there is no water coming out when I turn it on now. What should I do?

    Gene says September 23, 2019

    I would check the section “Slow/no water flow from faucet & low pressure” on this page.

Bren says September 29, 2019

I have an evolution ro sustem and my filtered water that comes out of the blue hose was working fine it slowed to a trickle? The black hose also lost pressure. For some reason the psi still says 40 sometimes close to 60 when my well turns on. Yet the flow is hardly there. How can i fix this?

    Gene says September 30, 2019

    Check the section Slow/No Water Flow From Faucet & Low Pressure on this page.

Karen Pearson says November 11, 2019

Can you help me with a pure water technology water system ? Its pouring out the ro drain

    Gene says November 12, 2019

    Water will run down the drain line as long as the tank is still filling.

chris says January 26, 2020

my reverse osmosis is not shutting off and it keeps throwing drain water. I have changed the pressure valve but to no avail. hence I am shutting it off as I need it but it very inconvenient. Help please.

    Gene says February 10, 2020

    Check “System Drains Constantly (Drain Line Keeps Running)”-section.

Gustav says July 28, 2020

I replaced filters on my 5 stage system, drained and cleaned the tank as instructions on google. But now it does not top up and keep the tank full when you use water. Only after the tank is empty does it start to filter again and you have to wait about 2 hours to fill. What can the problem be?

    Gene says August 11, 2020

    Maybe the tank pressure is too high?

David jose says September 2, 2020

After installing a new membrane in the membrane hosing also, the pure water outlet is not allowing the proper water outlet, whereas drainage is done properly. What can be the issue and how to fix it? Waiting for your reply soon. Thank you

    Gene says September 4, 2020

    David, could you rephrase that question please?

Jim Hill says November 1, 2020

I am considering purchasing a Waterdrop tankless RO system but have one major concern. Our house is a seasonal residence and as such, the RO system can sit unused for 6 months at a time. I understand the G3 system has a holiday mode which flushes the unit after each 24 hour period of non-use. Is this going to be adequate to avoid bacteria build-up? If I select their G2 system, can I not simply remove the filters when not in use? Your comments would be greatly appreciated.

Rick Smith says November 10, 2020

We have had our RO system for 5 years. I have changed the filters each year and changed the membrane 6 months ago. Our water pressure is great for 4-5 seconds, we hear a clunk, and then the flow goes down to a trickle. We wait for a minute and then the same flow occurs -great for 4 seconds and then a trickle. Does it sound like a tank issue?

    Daveu says September 2, 2021

    Yes may be a tank issue , the bladder in the tank sometimes gets inverted and when starts to fill up or used makes a clunk sound

Nikia Denery says July 6, 2021

My fist filter (between pipe and water tank) keeps clogging. They only last about 2 weeks. We have a water softener and our water isn’t that hard to begin with. This is costing me a fortune!

Add Your Reply