Why Does My Reverse Osmosis System Run Out of Water?

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Reverse osmosis systems are incredibly effective at removing a broad array of contaminants from water, but like any mechanical system, they can occasionally have problems.

One of the more frustrating issues that can pop up is your RO system running out of water. This can have several possible causes, so you’ll have to do a little sleuthing to find the problem.

Let’s examine all of the possible causes of your reverse osmosis system running out of water, as well as how to get it running properly again.

Key Takeaways

There are a variety of reasons that reverse osmosis systems might run out of water. These are:

  • A partially closed feed water valve or storage valve
  • Too high or too low pressure in the storage tank
  • A ruptured air bladder
  • A clogged filter element
  • Low feed water pressure
  • A trapped air pocket
  • A broken flow restrictor
  • Kinked tubing
  • Poor feed water quality
  • And low water temperature

The solution to the issue will depend on the specific problem, but many of the fixes are simple and can be done on your own.

Why Does My Reverse Osmosis System Run Out of Water?

Your reverse osmosis system may run out of water due to one of the following reasons.

High Water Usage

As you may be aware, reverse osmosis systems are notoriously slow at filtering water. That’s why most residential systems feature a storage tank to collect and store a reserve of filtered water.

These storage tanks can only store so much water at once and once emptied, the reserve is gone. At this point, the system must filter water continuously to provide water out of the faucet. This results in a snail-like flow of water, which can lead one to believe the system is malfunctioning.

In reality, this is normal and will happen to any tanked system once the tank is emptied. If you’ve used an unusually large quantity of water, then this may be the cause of your issue.

The only thing to do in this instance is to wait for the storage tank to refill before dispensing more water. A typical 4-gallon storage tank will take between 2 and 4 hours to refill depending on things like your water pressure, filter and membrane condition, and water quality.

If you find yourself running into this issue frequently, you may want to consider purchasing a larger storage tank or adding a second tank to the system. Storage tanks are relatively inexpensive and not difficult to install on your own.

young girl opening reverse osmosis faucet

Feed Water Valve Is Partially Closed

The feed water valve is the valve connecting your home’s main water supply with the RO system. When it’s shut off, the system will not receive any water and resultingly won’t create any filtered water.

If the valve is only partially closed, then the system will receive some water, but not enough to keep it functioning optimally. To fix this, simply locate the feed water valve and turn it until it’s all the way open.

RO Storage Tank Valve Is Partially Closed

Another similar issue can occur when the RO storage tank valve is partially closed. This is the valve located on top of the storage tank and allows the water to flow in and out of the tank.

If you suspect this might be the issue, locate the storage valve, and turn it until you’re sure it’s fully opened. After that, wait for the tank to fill and test out the flow by opening the RO faucet.

Your RO Tank’s Storage Pressure Is Too High

RO storage tanks use internal pressure to integrate with the rest of the RO system. As RO systems are pressurized, storage tanks must be pressurized to a specific range (typically 6 to 8 psi) to work with the rest of the system.

When the tank’s internal pressure is too high, water from the system will not be able to enter the tank sufficiently, resulting in poor or no flow from the RO faucet. You’ll likely also notice more water than usual flowing down the drain line.

To fix this issue, you’ll need to release some pressure from the tank. To do this follow these steps:

  1. Shut off the feed water valve under your kitchen sink.
  2. Open the RO faucet and let the water run until no more comes out.
  3. Disconnect the tank from the system and take it outside or to a shower/tub.
  4. Open the tank valve, and allow the water to flow out. Then connect a bike pump to the pressure valve and pump out any remaining water.
  5. Now, use a tire pressure gauge to check the tank pressure.
  6. If it’s too high, simply hold the pressure gauge against the valve to allow air to escape.
  7. Periodically check the pressure until it reaches the correct level.

Your RO Tank’s Storage Pressure Is Too Low

This issue is more common than the one described in the previous step. Like any pressurized system, air will eventually escape from the tank, which lowers the tank pressure to below the desired range.

What happens in this instance is water from the system can enter and fill the tank, but it won’t flow to the RO faucet properly. This will lead to a weak or nonexistent stream from the faucet.

To fix this issue, you’ll want to follow the steps outlined in the previous section, except instead of removing pressure in the tank, you’ll need to add pressure.

This is done using a bike pump or air compressor attached to the pressure valve to increase the tank’s internal pressure. If using an air compressor, be sure to go slowly and check the pressure often to avoid overpressurizing.

The Air Bladder Inside the Storage Tank Has Ruptured

RO storage tanks use a rubber bladder to regulate internal pressure. Unfortunately, over time these bladders can rupture. When this happens, your tank will still fill, but you won’t be able to pump any water out of the RO faucet.

Unfortunately, due to the design of RO storage tanks, there is no way to repair a ruptured tank bladder, and you’ll need to replace the entire tank.

To figure out if your bladder is ruptured, you’ll need to repressurize your tank and test the flow. After repressurizing, if a full tank is only able to pour a glass or two of water before stopping, you can be confident you’re dealing with a ruptured bladder.

A Clogged Filter Element

A clogged pre-filter, post-filter, or membrane can lead to a blockage in the system. This is more common with pre-filters but can happen to any filter element. Filter elements and membranes have a recommended shelf life before needing replacement, and if you forget to replace your filter on time, clogging is likely.

To test if a clogged filter element is the source of your problem, you’ll want to shut off the feed water valve and remove the filter element in question from its housing. Then reconnect the housing, turn the feed water valve back on, and test the flow by running the faucet.

If the system is running normally, then there are good odds your filter element is clogged. Replace it with a new one.

Different Water Filter Cartridges and Membranes

Issues with Feed Water Pressure

RO systems require a certain level of water pressure to operate. Generally, 40 psi is the absolute minimum, while 60 psi is optimal. If the water pressure entering your home’s main water line is too low, it won’t have the necessary power to force water through the RO membrane.

If your issue is low or fluctuating water pressure, you may need to install a booster pump to increase the pressure flowing into the system.

Air Pocket

Occasionally, an air pocket – sometimes called an airlock – forms somewhere in the system. This can have several possible causes, but can usually be fixed without too much difficulty.

To fix an airlock, you’ll want to relieve the blockage. The first thing to try is closing the storage tank valve, opening the RO faucet, and allowing water to flow for several minutes.

If that method doesn’t relieve the airlock, then you’ll need to release the airlock manually. Turn off the feed water valve, and disconnect the tubing in the location you think the airlock is located.

A Malfunctioning Flow Restrictor

The flow restrictor is used to limit the flow of wastewater through the drain line. It’s required to maintain the water pressure inside the reverse osmosis membrane housing.

A malfunctioning or broken flow restrictor won’t create enough backpressure in the RO membrane and will allow excess water to flow down the drain line. This will lead to a lot of wasted water, and very little water making it to the RO faucet.

A malfunctioning flow restrictor will need to be replaced. The exact process will depend on your particular system, so check your owner’s manual or contact the manufacturer for specifics.

Kinked Tubing

Kinks or bends in tubing lines can lead to blockages in the system. This will slow down or block the flow through the system – leading too little to no water coming from your RO faucet.

This generally happens when the tubing connection is longer than necessary – which makes it more prone to forming kinks or bends.

If you spot a kink or bend in your tubing, turn off the feed water valve, open the RO faucet, and remove the kinked section of tubing. Then either cut it down to the correct length or replace it with a new tubing section.

Poor Source Water Quality

Water with high levels of dissolved solids can prematurely clog the filters and membrane of a reverse osmosis system. If your feed water is of particularly low quality, or it contains a high concentration of problematic contaminants like iron or water hardness, then you may need to install an additional pre-filter stage.

To determine if poor water quality is the source of your problem, the best thing to do is to get your water professionally tested. This will give you a precise result of impurities contained in your water and their quantities. Then, you can install additional pre-filtration if it’s needed.

Source Water Is Too Cold

Particularly cold feed water can cause an RO system to run slower than normal. This isn’t a common issue for most people, but if you live in a particularly cold climate or have poor insulation it can be a factor.

To remedy this issue, you can install a booster pump to increase the feed pressure. This will help compensate for the low temperature. Alternatively, you may need to add some type of heating to your water supply.

How Does a Reverse Osmosis System Work?

A reverse osmosis system works by forcing feed water through an ultra-fine mesh filter – known as an RO membrane. These membranes will block any contaminant down to just 0.0001 microns in size.

After separating the contaminant-filled wastewater from the clean filtered water, the two streams flow in separate directions. The wastewater flows down the drain line and into the drain, while the filtered water flows onto the rest of the system.

It’s worth pointing out that while RO membranes are very effective, they can’t remove everything. Sediment and chlorine in particular are harmful to RO membranes, so they must be removed before water can reach the membrane. As a result, RO systems typically feature both activated carbon and sediment pre-filters to remove these contaminants before they reach the membrane. Many RO systems also feature one or more post-filters.

If you have any thoughts about the question, why does my reverse osmosis system run out of water, please don’t hesitate to leave a comment below!

About the Author Alexandra Uta

Alex is a content writer with an affinity for research and a methodical attention to detail. Since 2020, she has fully immersed herself into the home water treatment industry only to become an expert herself. Alex has been using water filters and similar products for years which has gained her lots of hands-on experience.
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