Reverse Osmosis Tank Not Filling Up with Water? Here’s Why + Fixes

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Have you ever noticed after a long day at work that your reverse osmosis tank hasn’t filled up with water while you were away?

A few reasons can cause this to happen. Don’t worry, though—we’ve got you covered with some tips and tricks on how to fix the issue so that your RO tank is up and running in no time.

Keep reading to learn more about what could be causing a reverse osmosis tank not to fill up properly and how to troubleshoot it.

Key Takeaways

  • Valves might be closed – Check feed water valve and ensure it is fully open + open storage tank valve and leak detector valve to allow water to flow
  • Low feed water pressure – Use a pressure gauge to check feed water pressure in your plumbing system and install a booster pump if pressure is too low
  • Clogged filter elements – Replace clogged pre-filters or a damaged RO membrane
  • Inspect tubing for kinks and straighten any bends
  • Over or under-pressurized storage tank – Check tank pressure when empty and adjust if need be
  • Your tank might simply be empty due to recently high-water usage
  • Airlock – Release air from system by closing tank valve and opening RO faucet
  • Low-flow RO system – The system might simply be too small for the size of the storage tank

Why Is My Reverse Osmosis Tank Not Filling Up with Water?

There are a few common culprits that could be preventing your RO tank from filling up with water. Let’s take a look at each of them:

Shut-Off Feed Water Valve

One possible reason why your RO tank isn’t filling up with water is because the feed water valve has been shut off. This valve controls the flow of water into the RO system, and if it’s closed, no water will be able to enter. Make sure to check the valve and ensure that it is fully open.

Closed Storage Tank Valve

Another reason why your RO tank may not be filling up with water is because the storage tank’s valve has been closed. This valve controls the flow of water in and out of the tank.

If it’s closed, water won’t be able to enter the tank, and the system won’t be able to produce any more clean water. To fix this issue, open the tank valve and allow water to flow in.

Under Sink Reverse Osmosis System

Low Feed Water Supply Pressure

Reverse osmosis systems require a certain level of water pressure to function properly. The minimum pressure required is usually around 40 psi.

If the feed water supply pressure is too low, the system won’t be able to produce enough clean water to fill your tank. Instead, most of the water will simply go down the drain line.

You can check the feed water pressure in your home by using a pressure gauge. If the pressure is too low, a booster pump may need to be installed.

How to Test Home Water Pressure

Let’s quickly go through how to check water pressure in your home.

It’s important to know this because most RO systems need high enough incoming water pressure to function properly. The minimum recommended psi is 40, so if it’s lower than that, you may be having issues.

To test your home’s water pressure, you can use a pressure gauge. If you don’t have one installed already, here is what to do:

First, find a water spigot that is close to where the main water supply enters your home. Then, attach the pressure gauge to the spigot and turn on the water. The pressure gauge will display the current water pressure.

Clogged Filters May Need Replacing

Over time, the pre-filters in your RO system can become clogged with sediment, dirt, and other impurities. This can reduce water flow and pressure preventing the bladder tank from filling.

Bottom line: It may be time to replace your filters!

Clogged RO Membrane May Need Replacing

The RO membrane is responsible for removing dissolved solids and impurities from the water. If the membrane becomes clogged, it won’t let enough water through, and most of the water will go down the drain line instead of into the tank.

If you suspect that your membrane is clogged, you may need to replace it.

Kink in RO System Tubing

A kink in the tubing of your RO system can restrict water flow and pressure. Thus, inspect the entire length of the tubing and straighten out any kinks or bends.

Improperly Pressurized Bladder Tank

If the air pressure in the bladder tank is too high, it affects the amount of water that can be stored in said tank – it will impede water from entering. There is a similar effect if tank pressure is too low.

In order to fix this, you will need to disconnect and empty the tank. Once empty, check the tank pressure using a suitable gauge. Release some of the air from the tank if it reads higher than 6-8 psi (check tank label for more info). Likewise, increase pressure using a bicycle pump if it’s too low.

Ruptured Tank Bladder

If the bladder in the tank ruptures, water won’t be able to flow up to the RO faucet. To fix this issue, you’ll have to replace the entire tank.

Shut Off Leak Detector

Some RO systems are equipped with leak detectors that shut off the supply of water to the system if a leak is detected. If your tank isn’t filling up with water, it’s possible that the leak detector has been triggered. You’ll need to check the leak detector and reset it if necessary.

High Water Usage

If you’ve been using a lot of water, it’s possible that your tank is simply empty.


If you’ve recently changed the pre-filters or membrane in your RO system, it’s possible that air has become trapped in the system. This can create an airlock that prevents water from flowing. To release the airlock, what you usually need to do is close the storage tank valve and open the RO faucet. Tilt the system if need be.

Low-Flow RO System

If your RO system is simply too small and not providing enough flow or pressure, it may not be able to overcome the backpressure of your storage tank and fill it with water.

How to Determine Your System’s Water Flow Rate

To determine your RO system’s water flow rate, you’ll need to perform the following steps:

  1. Turn off any appliances or fixtures in your home that use water, such as faucets or washing machines, to ensure that water is not being used elsewhere in your home.
  2. Remove the aerator from your RO faucet.
  3. Close the storage tank valve.
  4. Open the RO faucet and let the water run for one minute. Collect the water in a container and measure the volume of water collected.
  5. Multiply the volume of water collected by 60 to determine the flow rate in gallons per hour. For example, if you collected 10 ounces of water in one minute, the flow rate would be 10 x 60 = 600 ounces per hour or approximately 4.7 gallons per hour.

plumber installing reverse osmosis system under sink

It’s important to note that the flow rate of your RO system can be affected by a number of factors, such as the quality of your water source, the age and condition of your system’s components, and how much pressure is in your water supply.

If you’re concerned about your system’s flow rate or have noticed a decrease in flow over time, you may want to inspect your system’s components or consult a professional for assistance.

How Long Does It Take to Fill an RO Pressure Tank?

Generally speaking, an RO pressure tank can take anywhere from 2 to 4 hours to fill, the time frame depending on a variety of factors such as the water pressure in your home, the flow rate of your RO system, and, of course, tank size.

It is generally safe to assume that filling an RO pressure tank takes several hours at least.

What Is the Lifespan of a Reverse Osmosis Storage Tank?

The lifespan of reverse osmosis water storage tanks is mainly determined by the water pressure in your house and how often you use the system. Generally speaking, a bladder tank should last up to 10 years with proper maintenance.

However, if you are seeing signs that your tank isn’t filling up with water, then it may be time to replace it, as even a small issue can cause significant damage over time – think leakage.

What’s a Reverse Osmosis Water Storage Tank and How Does It Work?

RO storage tanks are an integral part of the process when purifying drinking water using reverse osmosis. As the name suggests, reverse osmosis is a process whereby contaminated water is forced through a semi-permeable membrane to create purified water on the other side.

The RO tank acts as a storage vessel for the filtered water, allowing you to have an immediate supply of clean water when you need it.

Most RO systems are designed to fill the pressure tank at a slow and steady pace, which helps to ensure that the water is properly purified.

As the water enters the tank, it pushes against the air pressure inside the tank, which compresses the air chamber inside and allows the tank to store more water. At some point, backpressure coming from the storage tank overcomes the pressure from the RO unit and filtration stops. Only when water is pulled from the tank by opening the RO faucet does the purification continue.

If you have any thoughts about the question, why is my RO tank not filling with water, 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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