RO Tank Troubleshooting: A reverse osmosis storage tank is one of the most important components of a traditional under-sink RO system. It stores purified water and uses an internal air bladder to push that water to the drinking-water faucet when you open it.
When the tank isn’t working properly, you may notice low water pressure, slow faucet flow, a tank that won’t fill, frequent cycling, or little or no water from the RO faucet.
Fortunately, many RO tank problems can be diagnosed and corrected without replacing the entire system.
This RO tank troubleshooting guide explains how a reverse osmosis storage tank works, how to diagnose common problems, how to check tank pressure, when to add air, and when the tank should be replaced.
For broader system maintenance, see Revosmo’s Reverse Osmosis Maintenance Guide, which covers filter replacement, membrane maintenance, leaks, sanitization, pressure problems, and other common RO maintenance issues.
Table of Contents
- How Does an RO Storage Tank Work?
- Common RO Tank Problems
- RO Tank Troubleshooting Checklist
- How to Check RO Tank Pressure
- How to Adjust RO Tank Pressure
- Why Is My RO Tank Not Filling?
- Why Is My RO Tank Full but the Faucet Has Low Pressure?
- Why Is My RO Tank Empty?
- Why Is My RO System Constantly Draining?
- How to Tell If an RO Tank Bladder Has Failed
- When Should You Replace an RO Tank?
- How to Maintain an RO Storage Tank
- Frequently Asked Questions
- Final Thoughts
How Does an RO Storage Tank Work?
Traditional under-sink reverse osmosis systems commonly use a pressurized storage tank because the RO membrane produces purified water relatively slowly.
Instead of sending water directly from the membrane to the faucet, the system gradually fills the tank.
Inside the tank is a flexible bladder separating the stored water from compressed air.
When the tank fills, the water compresses the air inside the tank.
When you open the RO faucet, the compressed air pushes stored water out of the tank and toward the faucet.
This means tank air pressure is directly related to faucet flow.
A tank with incorrect air pressure may have plenty of water inside but still produce weak faucet flow.
EPA explains that as an RO storage tank fills, pressure inside the tank increases and approaches incoming water pressure. This “back pressure” is also involved in the operation of the automatic shutoff device.
Common RO Tank Problems
The most common reverse osmosis tank problems include:
| Problem | Common symptom | Likely cause |
| Low tank pressure | Weak faucet flow | Insufficient air pressure |
| Excessive tank pressure | Tank doesn’t fill properly | Too much air pressure |
| Tank won’t fill | Little or no stored water | Low feed pressure, filters, membrane or valve |
| Tank fills slowly | Long recovery time | Clogged filters or low pressure |
| Tank is full but faucet is weak | Low water flow | Incorrect tank pressure or restricted faucet |
| Tank repeatedly loses pressure | Pressure drops after adjustment | Damaged bladder or leaking valve |
| Water from air valve | Tank failure | Ruptured internal bladder |
| Tank feels unusually heavy | Poor water delivery | Possible bladder or pressure problem |
| Continuous drain flow | System never shuts off | Automatic shutoff or related component problem |
| Tank leaks | Water underneath system | Tank valve, fitting or tank damage |
The important point is that not every RO problem is actually caused by the tank.
A clogged prefilter, exhausted membrane, low household water pressure, kinked tubing, or malfunctioning automatic shutoff valve can create symptoms that appear to be tank problems.
RO Tank Troubleshooting Checklist
Before replacing the tank, work through these basic checks:
- Confirm the RO feed-water valve is completely open.
- Check household water pressure.
- Check for kinked or restricted tubing.
- Check whether the prefilters are overdue for replacement.
- Check the RO membrane’s service life.
- Determine whether the storage tank actually contains water.
- Empty the tank completely before checking its air pressure.
- Check tank pressure with an appropriate pressure gauge.
- Adjust tank pressure according to the manufacturer’s specifications.
- Inspect the tank valve and connections for leaks.
- Check the faucet and post-filter for restrictions.
- Determine whether water is continuously flowing to the drain.
- Test the tank valve for evidence of a failed bladder.
- Replace the tank if it cannot hold pressure or has a damaged bladder.
If the tank checks out but the RO system still has low production or poor pressure, continue troubleshooting the rest of the system.
How to Check RO Tank Pressure
Checking the tank’s air pressure is one of the most useful RO troubleshooting procedures.
However, the tank must be empty before you check or adjust its air pressure.
Checking pressure while the tank contains water can produce an inaccurate reading.
What you’ll need
You generally need:
- A low-pressure air gauge
- Bicycle pump or suitable hand pump
- Towel
- Access to the RO system’s tank valve
Avoid using excessive pressure or an inappropriate high-pressure compressor.
Step-by-step procedure
1. Turn off the RO water supply
Close the cold-water supply valve feeding the RO system.
2. Close the tank valve
Turn the valve on top of the storage tank to the closed position.
3. Open the RO faucet
Open the drinking-water faucet to release the water stored in the system.
Allow the faucet to run until water stops flowing.
4. Empty the tank completely
The tank should be as empty as possible before measuring air pressure.
If the tank is still holding water, gently adding air may help push the remaining water out through the faucet, depending on the manufacturer’s procedure.
5. Locate the tank air valve
The air valve is normally located on the bottom or side of the storage tank beneath a protective cap.
It resembles the valve found on a bicycle or automobile tire.
6. Check the pressure
Attach a low-pressure gauge to the valve and note the reading.
What PSI should an RO tank have?
There is no universal tank-pressure specification for every RO system.
For example, a Pentair RO manual specifies an empty-tank pressure of 5–7 psi, while another Pentair RO manual specifies approximately 7 psi.
Therefore, the safest approach is to use the pressure specified by your particular RO system manufacturer.
Never assume that 7 psi is correct for every RO tank.
How to Adjust RO Tank Pressure
If the tank pressure is below the manufacturer’s specification, you can generally add air using a bicycle pump or suitable hand pump.
To increase tank pressure
- Confirm the tank is completely empty.
- Remove the protective cap from the air valve.
- Attach your pressure gauge.
- Add a small amount of air.
- Check the pressure.
- Continue gradually until you reach the manufacturer’s recommended pressure.
- Reinstall the valve cap.
- Reconnect the tank to the system.
- Open the tank valve.
- Turn the water supply back on.
- Allow the tank to refill.
Pentair’s troubleshooting instructions similarly direct users to empty the tank and then check or adjust the air pressure, with one system specifying 5–7 psi when empty.
Don’t overinflate the tank
Too much air pressure can reduce the amount of water the tank can store.
If the tank pressure is significantly above the manufacturer’s specification, remove a small amount of air and check the pressure again.
Small adjustments are preferable to large ones.
Why Is My RO Tank Not Filling?
An RO tank that won’t fill can have several possible causes.
The first step is determining whether any water is entering the tank.
Possible causes include:
- Low household water pressure
- Closed feed-water valve
- Clogged sediment filter
- Clogged carbon filter
- Exhausted RO membrane
- Kinked tubing
- Faulty automatic shutoff valve
- Incorrect tank pressure
- Blocked flow restrictor
- Faulty tank valve
- Water supply problem
Pentair identifies a clogged prefilter or exhausted membrane as common causes of reduced or absent product-water flow.
Start with the filters
If your RO filters are overdue for replacement, replace the appropriate filters first.
EPA notes that many RO systems require prefilter replacement about every six months and membrane replacement approximately every one to five years, depending on water quality and use.
Check household pressure
The RO system needs adequate incoming water pressure to push water through the membrane.
EPA WaterSense recommends residential service pressure generally be maintained between approximately 45 and 60 psi for water-using fixtures.
If the home’s incoming pressure is significantly below the system manufacturer’s requirements, the RO system may produce water extremely slowly.
Why Is My RO Tank Full but the Faucet Has Low Pressure?
This is one of the most common RO tank complaints.
If the tank is full but only a small trickle comes from the faucet, the storage tank is a logical place to start troubleshooting.
Possible causes include:
- Low tank air pressure
- Incorrect tank air pressure
- Failed tank bladder
- Clogged post-filter
- Kinked product tubing
- Restricted faucet
- Partially closed tank valve
- Faulty tank valve
Test the tank pressure
Empty the tank and check the air pressure according to the manufacturer’s instructions.
If the pressure is low, adjust it to the specified level.
Then refill the tank and test the faucet.
If normal flow returns, the problem was likely related to tank pressure.
If the tank pressure is correct but faucet flow remains poor, investigate the post-filter, tubing and faucet.
Why Is My RO Tank Empty?
If you open the RO faucet and get little or no water, check whether the tank actually contains water.
An empty tank may indicate that the system isn’t producing enough water to refill it.
Possible causes include:
- Clogged prefilters
- Exhausted membrane
- Low incoming water pressure
- Kinked tubing
- Faulty shutoff valve
- Flow restriction
- Excessive water consumption
- Tank valve problem
Check the tank weight
A simple diagnostic method is to carefully lift the tank.
A tank containing several gallons of water should feel substantially heavier than an empty tank.
If the tank is light, the problem may be that the RO system isn’t producing enough water to refill it.
If the tank is heavy but faucet flow is poor, focus on tank pressure and the components between the tank and faucet.
Why Is My RO System Constantly Draining?
An RO system with a storage tank should normally stop producing reject water after the tank reaches its operating pressure and the automatic shutoff mechanism closes.
If water continuously flows to the drain even when the tank is full, the automatic shutoff system or another component may be malfunctioning.
EPA identifies the automatic shutoff device as an important component in tank-style RO systems because it stops incoming water when the storage tank reaches the appropriate pressure. EPA also notes that continuous discharge to the drain can indicate that the shutoff device needs replacement.
Possible causes include:
- Faulty automatic shutoff valve
- Incorrect tubing connections
- Faulty check valve
- Insufficient tank pressure
- Damaged or incorrectly installed components
- Pressure imbalance within the system
Continuous drain flow shouldn’t simply be ignored.
Besides wasting water, it can indicate that the RO system isn’t operating as designed.
How to Tell If an RO Tank Bladder Has Failed
The internal bladder is what separates the stored water from the tank’s compressed air.
If the bladder fails, the tank may no longer operate correctly.
One of the strongest warning signs
Water coming out of the tank’s air valve is a major indication that the bladder has failed.
An intact bladder should separate the water compartment from the air chamber.
If water reaches the air valve, the tank generally needs to be replaced.
Other possible signs include:
- Tank will not maintain air pressure
- Very poor faucet flow
- Tank repeatedly loses pressure
- Tank behaves differently after being repressurized
- Tank feels unusually heavy
- Water delivery becomes inconsistent
Before replacing the tank, make sure the problem isn’t simply an incorrect air-pressure setting.
When Should You Replace an RO Tank?
An RO storage tank doesn’t necessarily need replacement simply because it has low pressure.
Try adjusting the air pressure first.
Replacement becomes more likely when:
The tank cannot hold air
If you properly pressurize an empty tank but the pressure repeatedly falls, there may be a leak or internal bladder failure.
Water comes from the air valve
This strongly suggests an internal bladder problem.
The tank is physically damaged
A dented, corroded, cracked, or otherwise damaged tank should not be relied upon.
The tank repeatedly causes poor performance
If filters, membrane, tubing, valves and faucet are functioning correctly but the tank still cannot deliver water properly, replacement may be appropriate.
The manufacturer recommends replacement
Follow the manufacturer’s service recommendations for the specific tank and system.
How to Maintain an RO Storage Tank
Regular maintenance can help prevent many storage-tank problems.
Periodically drain the tank
EPA recommends periodically draining the RO storage tank, noting that doing so also helps the membrane maintain the pressure required for contaminant removal.
A full tank drain can also provide an opportunity to evaluate whether the system is refilling normally.
Follow the manufacturer’s sanitization instructions
Many manufacturers recommend periodic sanitization of RO storage tanks.
EPA notes that many manufacturers recommend annual tank sanitization to reduce the risk of bacterial growth.
Do not introduce bleach or another sanitizer into an RO system unless the system’s manufacturer specifically instructs you to do so.
Some sanitization procedures require removing the membrane and filters before the sanitizer is introduced.
Replace filters on schedule
Clogged prefilters can restrict water entering the membrane and ultimately affect tank production.
Follow the manufacturer’s filter-replacement schedule rather than waiting until water production stops.
Check for leaks
During filter changes and other maintenance, inspect:
- Tank valve
- Tubing connections
- Faucet tubing
- Filter housings
- Tank body
- Automatic shutoff connections
Even a small leak can affect system performance.
Keep a maintenance record
Record:
- Filter replacement dates
- Membrane replacement date
- Tank pressure readings
- Sanitization dates
- Any unusual changes in water production
- Repairs or replacement parts
This makes future troubleshooting much easier.
RO Tank Troubleshooting: Symptoms at a Glance
Use this quick reference when diagnosing an RO storage tank.
| Symptom | Most likely areas to check |
| No water from faucet | Tank empty, feed pressure, filters, membrane |
| Very weak faucet flow | Tank pressure, post-filter, faucet |
| Tank won’t fill | Feed pressure, filters, membrane, shutoff valve |
| Tank fills very slowly | Filters, membrane, low pressure |
| Tank full but weak flow | Tank air pressure, post-filter, tubing |
| Tank loses pressure | Valve leak or failed bladder |
| Water from air valve | Failed bladder |
| Constant drain flow | Automatic shutoff system |
| RO system runs continuously | Shutoff valve, pressure or check valve |
| Poor taste after tank sits | Filter/membrane condition, sanitization |
| Tank leaks around valve | Tank valve or connection |
| Tank is unusually heavy | Possible pressure/bladder issue |
Frequently Asked Questions
How do I know if my RO tank is bad?
A tank may be failing if it cannot maintain its specified air pressure, produces water from the air valve, has a damaged bladder, or continues to provide poor performance after the rest of the RO system has been properly serviced.
How much air pressure should be in an RO tank?
The correct pressure depends on the tank and RO system. Some Pentair systems specify approximately 5–7 psi or 7 psi with the tank empty. Always follow the manufacturer’s specification for your particular system.
Should an RO tank be full of water?
A properly functioning tank-style RO system should store purified water when the system has completed its filling cycle. The amount of water stored depends on the tank’s design, incoming pressure, membrane production and operating conditions.
Why does my RO tank have water but no pressure?
The tank may have insufficient air pressure, or the internal bladder may be damaged. Empty the tank and check its air pressure according to the manufacturer’s instructions.
Can I add air to my RO tank?
Yes, many pressurized RO tanks can be repressurized through their air valve. However, the tank should be empty first, and you should use the manufacturer’s specified pressure.
Can too much air pressure damage an RO tank?
Excessive pressure can interfere with proper filling and may stress components. Never exceed the pressure specified by the manufacturer.
Why does my RO tank lose pressure?
If an empty tank repeatedly loses its air pressure, there may be a leak, defective valve, or damaged internal bladder.
How often should I drain my RO tank?
EPA recommends periodically draining the storage tank and notes that draining can help the membrane maintain the pressure required for contaminant removal.
Follow your system manufacturer’s specific maintenance recommendations.
Why does my RO system keep sending water down the drain?
Continuous drain flow can indicate a problem with the automatic shutoff device or another component affecting system pressure. EPA specifically identifies continuous drain discharge as a possible sign that the automatic shutoff device needs replacement.
Should I replace the tank or the membrane?
Don’t replace either component based solely on low faucet flow.
First determine whether the tank has the correct air pressure and whether the filters and membrane are within their service intervals.
A tank problem generally affects storage and delivery, while a membrane problem more often affects production rate and water quality.
Final Thoughts
A reverse osmosis storage tank is relatively simple, but a small problem with its air pressure or internal bladder can dramatically affect faucet performance.
When troubleshooting an RO tank, start with the basics:
- Determine whether the tank contains water.
- Empty the tank completely.
- Check the tank’s air pressure.
- Adjust it according to the manufacturer’s specifications.
- Check the tank valve and connections.
- Inspect the filters, membrane and tubing.
- Check the faucet and post-filter.
- Investigate continuous drain flow and the automatic shutoff valve.
- Replace the tank only when testing indicates the tank itself has failed.
Don’t assume that every pressure problem is a bad tank. EPA notes that low production and low pressure can be signs that an RO system needs maintenance, while clogged filters, membrane condition and other components can all contribute to poor performance.
For a complete maintenance strategy covering your filters, membrane, tank, leaks, sanitization and other common RO problems, continue to Revosmo’s Reverse Osmosis Maintenance Guide.
