Reverse Osmosis System Making Drain Noise? Find Easy Fixes Here!

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It’s a good idea to familiarize yourself with the normal operation of a reverse osmosis system and know what you can expect from them.

That way you’ll be able to identify potential issues, and you’ll know when noise coming out of such a system is not within the normal boundaries – such as excessive drain noise.

Wait, reverse osmosis drain noise isn’t normal? It could be!

Key Takeaways

Don’t be alarmed by draining noise from your reverse osmosis system by default.

Only if you hear drain noise 24/7 or if it’s very loud, there are some potential issues you should investigate for:

  • A misaligned drain saddle – realign
  • Siphoning in your tubing – shorten tubing
  • Too high/low feed water pressure – adjust
  • A broken ASO or check valve, or flow restrictor – replace
  • A clogged or oversized RO membrane – replace
  • Tank pressure issues – adjust

What Is Normal Drain Noise Made By a Reverse Osmosis System?

It’s normal to hear some of the water going down the drain when you start to dispense water from the reverse osmosis tank and the system starts filtering again to refill the tank.

However, this should only be temporary and it shouldn’t be too loud. If you’re hearing strange noises like that all the time, and they sound particularly loud, this could indicate an actual problem.

How to Fix Abnormal Reverse Osmosis Drain Noise

Fixing strange drain noises in your reverse osmosis system mostly comes down to identifying the problem and figuring out a straightforward solution to it. There are several potential causes for abnormal drain noise from your reverse osmosis system. Let’s have a look at those.

Off-Center Drain Saddle/Line

If the sound resembles hissing and is particularly loud, this could indicate that you might have a misaligned drain line. This line connects the reverse osmosis membrane outlet and the drain saddle. With time, the saddle might loosen and it could end up blocking the drain line either partially or completely.

Fixing this involves shutting off the water supply, allowing the drain line to flush, and removing the drain saddle. Check to see if there is any debris stuck in there, and align the drain saddle properly.


Siphoning issues might be caused in situations when the piece of tubing that runs between an air gap faucet and the drain saddle is too long. This will result in air filling up the drain line and making strange noises. If this is the case, you have to find a way to shorten the tubing – think cutting it.

plumber installing reverse osmosis system under sink

High Feed Water Pressure

Reverse osmosis systems require a lot of pressure to operate properly. However, it’s possible to actually have too much pressure in your system, which could cause it to eject excessive amounts of water when it’s filtering.

If you live in a rural area and rely on lots of long pipes, that’s very likely the cause. You will need to install a pressure regulator at your house’s feed line or at least add one to the feed line of your RO system.

RO System Constantly Draining

You might also have issues with your reverse osmosis system draining all the time. This can be caused by a number of factors, and it might require a more in-depth investigation.

Broken ASO or Check Valve

If the automatic shut off or the check valve is broken this will lead to constant draining of your reverse osmosis system.

Figuring out if that’s the case is very simple.

  1. You just need to fill the storage tank and dispense a few glasses of water from the faucet to reduce the pressure inside the tank. This will trigger the system and start the filtration process.
  2. At this point you close the tank valve, which would imitate a situation with a full tank and wait a few minutes. If water is still going down the drain, this probably indicates that one of the valves is broken.
  3. In order to find out which one, let the tank refill.
  4. Then, open the feed water valve. If water is still flowing down the drain, it must be coming out of the storage tank which indicates a malfunctioning check valve. No draining Then it’s the ASO that needs replacement!

Malfunctioning Flow Restrictor

One of the key components of a reverse osmosis system is the flow restrictor. It’s used to maintain pressure within the membrane by restricting the flow of water out of it and down the drain line. If the restrictor is broken, you might get large amounts of wastewater flowing down the drain all the time.

The most straightforward way to fix this is to simply replace the restrictor. Attempting to repair it could be too complicated in most cases.

Low Feed Water Pressure

As we mentioned above, reverse osmosis systems require a certain amount of pressure to operate correctly. You need to ensure that you have at least 40 psi of pressure for basic operation and around 60 for optimal performance. If the pressure is too low, this could cause issues with the process. In this case you might have to install a pump to increase the pressure manually.

Clogged Filter Element

You need to regularly replace the reverse osmosis membrane as it will clog up over time. This should usually be done once every couple of years. If your water is particularly heavily contaminated, you will have to replace the membrane more frequently. A clogged RO membrane means lots of water running down the drain.

Issues with the Storage Tank

You might also have issues with the pressure inside your storage tank. If that’s the case, you might have to look into repressurizing it. This is relatively simple, but should be done carefully because otherwise you might take it too far. Always use a pressure gauge to check the current status of the system (when empty!).

Under Sink Reverse Osmosis System

Oversized RO Membrane

If the reverse osmosis membrane is too large for your current system, this can also lead to issues. The simplest way to fix this is to just get an appropriately sized membrane. If you’re having issues finding the correct model, talk to a water treatment expert – they should be able to guide you through the process.

If you have any questions about reverse osmosis drain noise 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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