Scott Winfield
Written by Scott Winfield
Last Updated on

RO systems can sometimes experience issues that lead to drainage. While you can always hire a professional to fix your RO system, you can resolve many common problems on your own. To do this, you’ll first need to understand how the reverse osmosis system works.


Here are the most common reasons for reverse osmosis drainage:

  • Low pressure inside storage tank
  • Ruptured air bladder
  • Damaged shut-off valve
  • Broken check valve
  • Worn-out flow restrictor
  • Faulty RO system installation
  • Clogged RO membrane

In this article, we discuss all of these issues and provide guidance on how to fix them. By the end, you should be able to identify why your RO system is constantly draining and resolve the problem yourself.

1. Low Pressure Inside the Storage Tank Can Cause Drainage

Low water pressure is the most likely cause if your RO system is draining, so it’s the first thing you should check.

Plumber analyzing water pressure in storage tank
Plumber analyzing water pressure in storage tank

The RO system employs a high-pressure water pump to push water through the membrane, which is then stored in the storage tank. Maintaining pressure inside the tank is essential for keeping the system running smoothly. When the tank is empty, the air pressure inside should be between 6 psi and 8 psi.

If your filtration system has drainage issues, you need to check the PSI levels using a pressure gauge. If it’s lower than 6 psi, you need to increase it.

How to Fix Low Storage Tank Pressure:

To increase storage tank pressure, you need to re-pressurize the RO tank. This relatively easy process requires just two tools: a bicycle pump and a pressure gauge.

Here’s how you can do it:

Step 1: Turn off your water supply and shut off the pressure tank valve. Disconnect the tank and drain the remaining water.

Step 2: The water should drain quickly at first. Once the water flow decreases, you will need to insert air into the tank using a bicycle pump.

The more you pump, the more water will come out. Keep pumping until the tank is empty.

Step 3: Take the pressure gauge and check the pressure. If it’s still lower than 6 psi, you need to repressurize the air pressure valve.

Locate the valve stem first and carefully remove its cover. Remember, there’s a second valve directly connected to the RO membrane. Stay away from the second valve so that you don’t damage the unit.

Step 4: Use the bicycle pump or an air compressor to pump air into the tank. Keep checking the PSI gauge to make sure you’re not over-pressurizing it, as this can cause the tank to rupture.

Step 5: When the pressure reaches the standard level of 6-8 psi, stop pumping and close the pressure valve. Replace the removed parts and reattach the tank to the RO system. Turn on the flow and check if the drainage problem is fixed.

2. Ruptured Air Bladder Can Cause RO System Drainage

Even if the first method yields positive results, your RO system might start draining again after a few days. In that case, check the air bladder for damage. If the air bladder is damaged, there will be little or no water flow, even when the tank is full.

Plumber examining RO Storage tank
Plumber examining RO Storage tank

You can easily detect a ruptured air bladder by adding one cup of water to the tank at normal pressure levels. If the water flow decreases, your air bladder is definitely damaged.

If you don’t regularly maintain your RO unit, the air bladder might rupture due to excessive water pressure.

How to Fix a Ruptured Air Bladder:

Unfortunately, there is no way to properly fix a ruptured air bladder. If it’s damaged, your only option is to replace it.

3. A Damaged Shut off Valve Can Cause System Drainage

Reverse osmosis water is stored in the tank after it goes through the filtration process. When the tank becomes full, the automatic shut-off valve (ASO valve) is triggered to stop the flow. This prevents more water from entering the storage tank.

Shut Off Valve
Water Shut off Valve

When the ASO valve is broken or damaged, unwanted additional water flows into the RO system, causing the tank to leak. Fortunately, detecting a broken ASO valve is very easy.

Fill the tank and keep the tank valve open, then listen closely to hear if the water is draining. You can pull the drain line from the drain saddle to check if the water keeps draining. If it does, this means the ASO valve isn’t doing its job and is probably broken or damaged.

How to Fix a Damaged Shut-Off Valve:

To solve this problem, you will have to replace the broken ASO valve.

You can do it by following these steps:

Step 1: Dismount the RO system to gain better access to the valve, which is located at the back of the RO unit.

Step 2: Once you navigate the valve, take note of its configuration so that you can install the new one correctly. The top portion of the valve has in and out markings on it, while the bottom portion is held in place by screws.

Step 3: Remove all tubes connected to the ASO and reconnect them to the new valve. Make sure the new valve is connected in exactly the same way as the old one.

When you’re done, remount the RO unit and check if the water flows into the drain as before. If it doesn’t, you have successfully fixed your valve problem.

4. A Broken Check Valve Might Cause Drainage

The ASO valve shuts down automatically in order to reject extra water once the RO tank is full. The check valve serves to prevent rejected water from draining.

Check Valve

If the valve is broken, the water pressure will push the water into the drain pipe, causing constant drainage.

How to Fix a Broken Check Valve:

Check valves are very affordable and can be easily replaced. So, the best course of action is to get a brand new one.

There are two types of check valves available on the market: straight and 90-degree check valves. We recommend going for the 90-degree valves, as they’re easier to install.

There are three main things that you should consider before installing a new check valve:

Step 1: Make sure you choose the right valve for your pipe size, pipe orientation, water flow direction, and flow rate. If none of these align with your setup, you will most likely experience inefficiencies or unnecessary wear and tear on your new valve.

Step 2: Pay close attention to where you need to install the valve in the piping line. Plus, bear in mind that some valves aren’t meant for vertical piping runs. Additionally, you need to ensure that the valve is at least five pipe diameters removed from the elbows and other valve fittings. By doing this, you are significantly reducing the potential turbulence that might occur.

Step 3: The valve should always be aligned with the flow arrow. In most cases, you will be able to find the flow arrow marked on the valve itself. Align this with the water flow, and you should have no problems whatsoever.

5. Worn-Out Flow Restrictor

The flow restrictor is a crucial component of an RO system, as its job is to gauge when and how much water drains from the tank.

Worn-Out Flow Restrictor
Flow Restrictor

When the restrictor wears out, the high-pressure water flows directly into the drain. This causes the pressure inside the system to decrease.

How to Fix a Worn-out Flow Restrictor:

To prevent drainage issues, you should replace the restrictor annually regardless of whether it’s worn out.

Follow these easy steps to replace your old flow restrictor:

Step 1: Locate the restrictor by looking behind the membrane housing on the black waste water line. Then, turn off the feed water and the tank valve.

Step 2: As the restrictor is located between the black tubing and the drain saddle, you need to disconnect the black tubing from the RO system.

Step 3: Remove the worn-out restrictor from the black tubing and replace it with a new one. Make sure the arrow on the restrictor is facing toward the drain saddle. Reconnect the black tubing to the system and check if the water is still draining.

6. Faulty RO System Installation Can Cause Drainage

If you can afford it, it’s always better to hire a professional to install your RO system. The slightest misplacement can lead to major issues such as constant water draining.

Plumber Following RO Installation Checklist
Plumber Following RO Installation Checklist

If you place the wrong tubing on the wrong fitting or don’t place a component in the right direction, the feed water could flow into the drain line.

How to Remedy Faulty RO System Installation:

If you can’t afford or don’t want to employ a professional for the installation, follow the product’s instructions closely. Take all the time you need to connect all the components correctly.

If you’ve already installed the RO system, dismount it and reinstall it again. This time, make sure that you double-check everything in the user manual as you go along.

7. Clogged RO Membrane Can Cause Drainage

Some parts of RO systems warrant regular replacements to pump out clean water as desired.

Because the RO membrane filters unwanted residue, it can accumulate different kinds of debris, dirt, contaminants, and other impurities over time.

Clogged RO Membrane
Worn-Out RO Membrane

You need to flush and replace the membrane regularly so that this accumulation doesn’t eventually lead to blockage.

If the membrane gets clogged, the pure water won’t be able to pass through and will go directly to the drain pipe.

The entire system can fail because of one clogged or bad RO membrane.

How to Fix Clogged RO Membrane:

You can easily solve this problem by flushing regularly or replacing the RO membrane.

To replace an RO membrane, follow the specific instructions included in the unit’s manual.

How to Fix Clogged RO Membrane:

You can easily solve this problem by flushing regularly or replacing the RO membrane.

The process of replacing a RO membrane is complex, so you will want to hire a professional to do the job.

In Closing

The best way to prevent your RO system from developing drainage issues is to maintain it regularly. This typically involves flushing the system, checking for faults, and replacing the membrane when it’s worn out or clogged.

Don’t hesitate to hire a professional if the task at hand is more than you can handle, and always check the manufacturer’s instructions before you try to resolve an issue with your system.

If you’ve reached the point where you need to replace the entire unit, check our reverse osmosis systems buyer’s guide for guidance on the best RO systems currently on the market.

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Scott Winfield
Scott Winfield
My name is Scott Winfield and researching and writing about water filters and other strategies to purify water has become my full time passion in recent years. I'm glad that you found our site and you can look forward to authoritative and well researched content here to help you get the best in water.
  1. I didn’t get the answer I was looking for. My question that I need to have Is The water that drains out of the osmosis system suitable for drinking or cooking. We have a softener system along with the osmosis system
    We are in the country and on a well that trickles into a cistern that we have to fill at $200.00 a fill cause of periods of when the well goes dry. Right now I am collecting the drainage water from the osmosis system so I don’t waste so much water going down the drain. Can I use that water suitable to use. Please help me with this problem

    1. Hi Mary, the water that the RO system is draining out is the “waste water” that contains all of the impurities that it’s passing. Maybe I don’t understand your question right. If I did, however, you definitely do not want to use this waste water if the point of the RO system you have is that you require pure water for your household needs.

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