Reverse Osmosis Troubleshooting Guide

Reverse Osmosis Guide

Reverse osmosis (RO) systems can run for years without any problems. When problems do arise, though, they are usually easy to diagnose and fix.

Your RO system has several parts that work together to provide you and your family with clean water. Therefore, you need a systematic approach to troubleshooting your system that will help you eliminate possible issues.

Main Components of a Reverse Osmosis System

Reverse Osmosis System MembraneMembrane: The membrane operates under pressure, and without adequate pressure, TDS rejection and water pressure will be negligible.

Filters: Your RO system contains two different filters: prefilters and pro-filters. The prefilters protect your system from chlorine and other harmful sediments. Chlorine causes oxidation that destroys the membrane material. On the other hand, deposits can clog or damage the flow restrictor. Pro-filters allow fresh water to pass through carbon before they enter your ice maker, faucet, or refrigerator.

Check valve: This filter is located at the membrane water outlet. Its primary purpose is to protect the RO membrane from backpressure. The check valve also allows pressure to build up when the storage tank is filled and activate the ASO valve. Without the check valve, your RO system won’t shut down, and this can cause backflow, which may damage the RO membrane.

Flow restrictor: It provides resistance and creates pressure on the RO membrane while metering the rate of water flowing to the drain. Its size will vary depending on the membrane output rating. When the wrong size is fitted, it disrupts membrane output.

Automatic shut-off (ASO) valve: This is a device that monitors the feed and tank pressures. After the pressure reaches two-thirds of the line pressure, the automatic shut-off valve closes and stops water from flowing.

Feed pressure: Water pressure entering your reverse osmosis system is vital to your system’s overall performance.

Storage tank: Your RO system uses a pressure or hydro-pneumatic storage tank. The tank is divided into two main chambers, one for air, and the other for water.

Drain saddle: Your RO system has a drain that disposes of contaminants. The sink drain is connected to the waterline with a drain saddle.

Common RO System Problems and Their Solutions

Reverse Osmosis SystemSome of the common RO system problems include:

  • System drains constantly
  • Dripping or leaking system
  • No, little, or slow water from the faucet
  • Noisy gurgle
  • Bad taste and odor in the water


System drains constantly

Your reverse osmosis system relies on pressure. Feedwater gets into the RO system, gets purified and is stored in the storage tank. When the storage tank fills up, it triggers the ASO valve to shut. The ASO valve stops more water from entering into the RO system. The check valve also comes into play and prevents water from flowing through the drain line.

In case the storage tank has low pressure, or the check and automatic shut-off valves are broken, water may continue flowing down the drain. The ASO valve will only perform properly if the flow restrictor, membrane, check valve, and tank are all working correctly. When broken, your system will waste a lot of water and produce an annoying sound.

To fix this problem, you have to conduct two tests. However, start by measuring the tank pressure using a pressure gauge. Ensure that the storage tank is full before you measure the pressure. The pressure should be anywhere between 35 and 40 psi. In case the pressure is lower, it is an indicator that either the check valve or the shut-off valve are broken and need to be replaced. Below are the two tests that you can perform to determine whether the shut-off and check valves should be replaced.

Test 1

The purpose of this test is to determine if the ASO valve and check valve are performing correctly.

  • Lower the storage tank pressure by releasing about 20 Oz of water from the faucet. This will trigger your RO system to start purifying water to refill the tank.
  • Close the tank valve to mimic a full storage tank.
  • Give your RO system about 5 minutes to process the water.
  • Finally, check whether the water has stopped flowing down the line.

In case the water has stopped flowing, then it means the valves are functioning properly. If the water continues flowing, then it is a sign that the valves are broken.

Test 2

If the valves are broken, proceed to perform the following test:

  • Open the tank valve when the tank is refilling.
  • Shut-off the feed water valve.
  • Check whether water is flowing down the drain line.

If you find that water is still flowing from the tank, then the check valve is broken, and it should be replaced. On the other hand, if there’s no water flowing from the tank, then the ASO valve isn’t functioning correctly.

Dripping or leaking system

Leaky FaucetIn most cases, you can identify what’s causing your system to leak by checking all connections and making sure that they are tightened.

Leaky faucets

Is your faucet leaking or dripping for no apparent reason? This is an indicator that some parts of your RO system are loosely fitted. Tighten all connections and check whether the tubing is pushed further into the ports. In case the leaking is coming from below the faucet stem, then you will have to replace the piece.

Leaking filter or membrane housing

A worn-out or misplaced rubber O-ring is the most common cause of a leaking filter or membrane housing. To fix this:

  • Start by closing the feed valve to stop water from flowing into the system.
  • Close the tank valve
  • Remove the leaking filter housing.
  • Check the O-rings and replace them if they’re cracked.
  • Place the O-rings correctly.
  • Screw back the filter housing tightly.
  • Open the feed water valve.
  • If you find that the filter housing is still leaking, replace it as it may be damaged.

Over time, the membrane housing cap may also come loose and displace the O-ring. Therefore, ensure that you periodically retighten it.

Other reasons why your reverse osmosis system may be constantly draining include:

  • Feed water pressure that is below 40 psi. You can use a pressure pump to increase the pressure levels.
  • After using your system for several years, the flow restrictor may wear down and cause your system to run continuously. Replace the flow restrictor to fix this problem.
  • Poor installation of your RO system is one of the main reasons why water may continue draining down the drain. Manufacturers often recommend that you hire a professional to install your system. However, if you choose to install the system yourself, read the installation manual carefully. Ensure that all parts are in the right position before you can operate the RO system.

Air gap leaks

Your RO system has an air gap which prevents drain water from flowing back into the RO system. If you find that the air gap hole is leaking, then the drain line has been blocked by debris that have accumulated in the drain.

Typically, water in your RO system will flow from the tank to the faucet and then fall through the air gap. When the drain line gets clogged, it will result to back pressure which will push the water through your faucet and spill all over the sink. Although this may sound like a bad thing, it is an easy fix. All you need to do is to clear the drain line so that water can flow freely. You can do this using a pipe cleaner or a wire brush. Ensure that you also clean the drain saddle.

Frequent use of your system may also result in shifting of the drain saddles, which can also restrict water flow. Therefore, after cleaning the drain line, ensure that you check the drain saddle. In case it has shifted, realign it so that it is in line with the drain line hole.

No, little, or slow water from the faucet

RO System Under SinkIf you have had your RO system for some years and you find that your system suddenly doesn’t produce as much water as it used to, it means that your system has either low pressure or low water volume. The main cause of such a problem is a malfunctioning storage tank. Your storage tank has an air bladder that increases pressure as more water enters the tank. If there’s a leakage, the bladder won’t build up enough pressure. This may result in little or no water at all.

To solve this problem, start by lifting the storage tank to see whether it’s full. A full RO storage tank will weigh approximately 28 lbs. If the storage tank is full, then the problem is most likely inside the tank. Next, measure the pressure of your storage tank. An empty storage tank will have a 6 to 8 psi. In case the pressure is lower, then you have to repressurize it. If the problem recurs after a few days, it means the bladder inside the tank may be damaged, and you will have to replace the whole storage tank.

Other causes

Slow water from your faucets may also indicate low feed water pressure that is below 40 psi. To fix this problem, you will need a booster pump. Other possible causes may include:

  • A clogged flow restrictor
  • A poorly seated RO membrane
  • An empty tank
  • Bent tubing
  • A closed tank or feed water valve

A bad RO membrane or clogged filters – Clogging often occurs when the membrane has processed hard water. To fix the problem, you can either replace the membrane or install an additional pre-treatment system that will soften the water before it enters your RO system.

Noisy gurgle

When you install your RO system and use it for the first time, or you have replaced a filter cartridge, you might hear a loud noise as water runs to the drain. This isn’t something that you should worry about. The noise is produced by air as it is being pushed out of your RO system. However, the sound should disappear after a few days. In case the noise persists, check whether everything is properly hooked up.

Check the tubing and ensure that it is set straight. Also, inspect for any restrictions that may be interrupting water flow in the drain tube. If your RO system is still noisy, check for gaps. In case there are any faults, have them corrected.

Bad taste and odor in the water

Dirty or Bad Tasting WaterWhat could be worse than wanting to quench your thirst only to find that the water has a bad taste and odor? While the purpose of an RO system is to provide you with pure and good tasting water, sometimes your system may add a strange taste and odor to the water. After using your system for some years, you may find bad taste and odor in water which is brought along by the accumulation of biofilm in the water filtration process. To get rid of biofilm, change the filters, clean the storage tank, and replace the membrane.

When you replace the RO membranes and filters, make it a point to replace them at least twice every year. Replacing these components on a regular basis will prevent the accumulation of germs in your RO system. Remember also to sanitize your storage tank every time you replace the filters and membranes.

To prevent the accumulation of germs both in your system and in the water, it is recommended that you install a unit that features a modular filter. Such a system will dispose of the entire filter and membrane housings. While this is the only proven way to prevent the accumulation of pathogens, these systems are very expensive and require higher maintenance. However, by installing such a system, you won’t have to ever worry about drinking contaminated water that may cause health problems.


Now you know some of the most common RO system issues and how you can solve them. It’s important to note that you can avoid most of these issues by doing maintenance on your system at least once every year. Regular maintenance will not only keep your system running smoothly, but also save you money as you won’t have to handle serious problems.