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Why Is My Reverse Osmosis Tank Not Filling Up?

Note: This post may contain affiliate links. This means that at no cost to you, we may receive a small commission for made purchases.

Reverse osmosis systems are very important for our daily lives. We use them to purify drinking water, clean our dishes, and even make ice cubes.

But did you know that there are many different types of reverse osmosis systems? In this article, we’ll explain each type and help you choose the right one for your needs.

What’s A Reverse Osmosis Tank?

Reverse Osmosis Systems are used to purify water by removing dissolved minerals and other impurities.

A reverse osmosis system consists of an external filter cartridge (the membrane) and an internal filter cartridge (the diaphragm).

Water passes through the membrane into the internal chamber. As the water moves through the membrane, the contaminants pass through the membrane and collect in the internal chamber.

When the internal chamber fills up, the water stops flowing. To start the process again, you must empty out the internal chamber.

A reverse osmosis tank has a butyl lining. Butyl stops the stored purified water from contacting the tank’s metal casing. 

Pressurized air pumps water into your faucet. The design of Reverse osmosis (RO) is meant to fit below your sink.

Reverse osmosis tanks have different capacities. Usually, the capacity stated by manufacturers is more than what the tank actually holds.

For example, a tank labeled 4 gallons might contain 3 gallons of water. The rest of the space is occupied by metal and air bladders.

How Do Reverse Osmosis Systems Work?

A reverse osmosis system removes impurities from tap water. Pre-filtering removes large particles, while the semipermeable membrane eliminates dissolved solids.

Water flows through the semipermeable membrane until the storage tank fills. Reverse osmosis systems use a lot of energy.

Reverse osmosis systems have post-filters to clean up the stored water before it goes into your drinking water faucets.

Carbon filters remove bad tastes and smells. Eventually, you’ll get the best tasting water possible

Reverse osmosis (see also ‘Reverse Osmosis Vs. Distilled Water‘) systems are used to purify drinking water. Reverse osmosis systems use pressurized air to force water through membranes.

These membranes filter impurities from the water. Reverse osmosis is typically installed in homes or businesses.

Pressurized air is used to provide purified water into your home’s faucet on demand. No booster pump should be needed.

A reverse osmosis tank consists of two chambers – a water chamber and an oxygen chamber.

These two chambers are separated by a bladder. As the size of the tank increases, the chambers’ positions change.

Reverse Osmosis (RO) systems use high pressure pumps to force water through membranes. This process removes impurities from the water.  An RO tank does not need an electric pump to function.

However, without a pressurized air chamber in the tank, water won’t flow into the faucets.

You’ll need to install a delivery pump if there isn’t enough pressure to push water from the tank and into the faucet.

RO tanks work without electricity or a pump because there is a pressurized air chamber inside the tank.

The water will fill the tank, before moving into the faucet when the tank needs to be emptied.

Reverse Osmosis units are used to purify drinking water. RO filters remove impurities such as chlorine and other chemicals from tap water.

Water is pumped into the RO filter, then purified by passing over membranes. The purified water flows out of the back of the unit and into a storage tank.

This allows users to store water for later use. Waste water is then sent to a drain. Purified water is stored in a pressure tank until needed.

If the RO system fails, call a plumber to fix it. Typically, it takes about two to four hours to fill a reverse osmosis storage tank (2.8 gallon or 10.6 liters)

Why Is My Reverse Osmosis Tank Not Filling Up?

Water tanks should be completely filled within two to four hours. If the tank doesn’t fill up, check the pressure gauge. If there is no pressure, check the valve.

If the valve is open, close it. If the valve is closed, check the pressure relief valve. If the pressure relief valve is open, shut it off.

If the pressure relief is still open, then the problem is likely with the pump. Try replacing the pump if possible. If the pump is not replaceable, call a plumber.

Why Isn’t It Filling?

Reverse Osmosis systems require high pressure to function properly. A low pressure could mean that you need to install a booster pump for more pressure. 

Water supply valves must be checked regularly. If there is any problem with the system, you should contact your service company.

Check the water supply lines to make sure they’re straight and not kinked. If they are kinked, then you need to call your service provider.

Water Pressure

Your water supply may be too low. You should check your pressure before installing a new water system. A booster pump could help if your current system isn’t working properly.

Check the water-supply valves and ensure they are fully open. Look for any kinks in the pipes.

Water kept in the RO tank doesn’t flow into the fountains because the pressure is extremely low.

Conversely, water that flows from the filter doesn’t come into the RO tank because the pressure is too high.

You can check the pressure of the tank, but you first need to shut down the water supply.

Then measure the tank’s air pressure by turning off the water valve. You then use a bicycle pump to pressurize the tank. Once the pressure reaches 15 psi, you know that the tank is full of water.

Once the tank is empty, put air into it. The pressure gauge can monitor how much air you’re pumping into the tank. Then,switch the water supply valve off.

Open the tap and let the water drain. Remove the old filters and replace them with the new filters. You then need to re-screw the filter housings and close the valves.

For most RO systems to operate effectively, the ideal water pressure should be between 40 and 80 PSI. If your pressure drops below 40 psi, then water cannot flow through the RO membranes.

A booster pump is required if the incoming water supply pressure is too low for the RO system to operate properly.

Generally speaking, filters should be replaced every 12 months and the reverse-osmosis membrane every 24 months, but you may want to replace them sooner if they’re showing signs of wear.

A clogged filter is usually the main culprit when your RO system is filling slowly. The tank pressure should be at 7 psi when empty.

If your tank bladder is ruptured, you will need to replace it. More tips available in RO Troubleshooting Guide.

Inspect The Storage Tank

Water enters the tank when the pressure is 8 lbs. Pressure in the tank must be checked before using the water.

If pressure is too high, water won’t flow out of the filter. If pressure is too low, water won’t flow inside the tank.

Water should be supplied to the RO unit by a properly installed pipe. A kinked pipe will stop water flow and cause the unit to fail.

Replace The Filters

Shut the water supply valve and open the RO tap. Allow the tank to empty. Remove both the pre and the post filters.

Replace the old filters with new ones. Screw them back into place. This process should be done every month or two to ensure proper operation.

Check the water supply valve after 3 hours. If you still can’t get water out of the tap, then you’ll need to replace the RO Membrane.

Inspecting the unit’s water supply lines will help you determine if there are any problems with the system.

Kinks in the pipes may cause an interruption in water flow, preventing the unit from operating properly.

What Is Reverse Osmosis?

Reverse osmosis is a filtration method used to purify drinking water. It uses a semipermeable membrane to remove contaminants such as chlorine, lead, pesticides, herbicides, heavy metals, bacteria, viruses, and other impurities from the water.

The process begins with the installation of a special membrane inside a container called a “RO unit.” Water flows through the membrane from one side to the other.

As the water passes through, contaminants are trapped on the opposite side.

The purified water is then collected and stored in another container. In order to maintain its effectiveness, the membrane needs to be cleaned periodically.

The membrane consists of a thin layer of plastic that allows only pure water molecules to pass through.

When contaminated water is introduced to the membrane, the contaminants become attached to the surface of the membrane.

Over time, the contaminants build up and block the pores of the membrane. This causes the membrane to lose its ability to separate clean from dirty water. At this point, the membrane requires cleaning.

When the membrane becomes blocked, the water source is turned off and the water in the tank is drained.

The membrane is removed from the tank and placed in a solution of bleach and water.

The membrane is rinsed with fresh water until all traces of bleach have been washed away. Afterward, the membrane is returned to the tank and reattached.

Is It Safe For My Family To Drink Reverse Osmosis Water?

Yes! Reverse osmosis (see also ‘Is Reverse Osmosis Water Acidic? How To Test Yours‘) systems produce high quality water that is virtually free of harmful chemicals and tastes great.

The water is also safer than bottled water because it doesn’t contain BPA (bisphenol A), which is found in many plastics.

What Are The Benefits Of Reverse Osmosis?

Reverse osmosis systems have several advantages:

  • They do not produce any waste products.
  • They use less energy than conventional methods.
  • They provide clean, safe drinking water.
  • They reduce the amount of time needed to fill up a glass of water.
  • They are more efficient than distillation because they don’t require heating.
  • They are very economical.

What Are The Disadvantages Of Reverse Osmosis Water Treatment?

There are some drawbacks to reverse osmosis water purification:

  • They are relatively expensive compared to other types of water treatment.
  • They take longer to treat large amounts of water.
  • • Some people find that their water tastes different from untreated water.
  • There is no way to know how much contaminant removal has been achieved until the water has finished being treated.


Hopefully, this guide has helped you find out why your reverse osmosis tank isn’t filling up!

author avatar
Anthony Barnes
Anthony Barnes is the founder of Water Heater Hub and a second-generation plumber by profession. Before developing Water Heater Hub, Anthony Barnes was a full-time plumber, and he has undertaken a wide variety of projects over the decades. As a second-generation plumber, it was easy for Anthony to get used to the technicalities of all from a tender age


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