A reverse osmosis tank is the heart of any RO water purification system, ensuring you have clean, refreshing water on demand. According to the Centers for Disease Control and Prevention (CDC), reverse osmosis is one of the most effective household treatment methods for reducing specific contaminants such as nitrates, arsenic, and some microbial threats, provided the system is properly installed and maintained. This guide reveals everything homeowners need to know about a reverse osmosis tank—from how it works, to troubleshooting, to sizing and maintenance. Getting this single component right can make all the difference in your daily access to high-quality drinking water.
What Is a Reverse Osmosis Tank?
A reverse osmosis tank, often called an RO storage tank, is a pressurized container that holds purified water produced by your reverse osmosis system. Think of it as a small water reservoir located under your sink.
The reverse osmosis filtration process is very slow. It can take several minutes to produce a single glass of filtered water. Without a storage tank, you would have to wait a long time every time you wanted a drink. The RO water tank solves this problem by collecting the purified water ahead of time. When you turn on your special RO faucet, the tank delivers this stored water instantly, providing a steady stream for drinking or cooking. Its key role is to ensure you have a convenient supply of purified water whenever you need it.
How Does a Reverse osmosis Tank Work?
Have you ever wondered what goes on inside that metal or plastic dome under your sink? The mechanism is simple yet effective, relying on air pressure to do the work.
Inside every reverse osmosis tank are two main compartments separated by a flexible rubber sheet called a bladder or diaphragm.
- Air Chamber: The bottom part of the tank contains a sealed chamber of compressed air. Before any water enters, this chamber is pre-charged with a specific amount of air pressure, typically between 5 and 8 pounds per square inch (psi).
- Water Chamber: The top part is where the purified water is stored. This is the chamber connected to the RO system’s water line.
Here’s the process in action:
- Filling: As your RO system produces purified water, it sends it into the water chamber of the tank.
- Compression: The incoming water pushes down on the rubber bladder, compressing the air in the chamber below it. This builds up potential energy, much like compressing a spring. The more water that enters, the higher the pressure inside the tank becomes.
- Dispensing: When you open the RO faucet, the built-up air pressure in the bottom chamber pushes back up against the bladder. This forces the stored water out of the tank, up through the tubing, and out of your faucet. This is why you get a smooth, consistent flow of water from the tank.
Essentially, the air acts as a spring to push the water out. Once the tank is nearly empty, the air pressure returns to its original pre-charge level, and the tank is ready to be filled again by the water from the RO system.
Types of Reverse Osmosis Tanks
Not all RO tanks are created equal. They come in different sizes, materials, and even orientations. Understanding these differences helps you choose the right one for your home’s water filtration needs.
| Feature | Standard Tanks | Specialized Tanks |
| Material | Steel: The most common type. Durable with a painted exterior to prevent rust. Inside, a polypropylene liner and butyl rubber bladder prevent water from touching the metal. | Plastic: Lighter weight and completely rust-proof. A good choice for humid environments or areas with corrosive air (e.g., near the coast). |
| Orientation | Vertical: The standard design, which stands upright under the sink. Most common for residential RO drinking water systems. | Horizontal: Designed to lie on its side. Useful for tight spaces or unconventional cabinet layouts where a vertical tank won’t fit. |
| Capacity | 2 to 4 Gallons: The typical storage capacity for a home. A 4-gallon tank will actually hold about 2.5 gallons of usable water due to the space taken by the air bladder. | 10+ Gallons: Large-capacity tanks are available for households with high water usage, or for connecting to multiple points of use like refrigerators and ice makers. |
Tank-Based vs. Tankless RO Systems
The biggest decision is whether you want a system with a tank at all.
Tank-Based RO Systems (Traditional):
- Pros: Provides instant access to a large volume of water. Simple, reliable technology. Less expensive upfront.
- Cons: Takes up under-sink space. The stored water can sometimes develop a slight "tank taste" if not used regularly. It also has a slower water production rate that relies on storage.
Tankless RO Systems (Direct Flow):
- Pros: Delivers freshly filtered water on demand—no storage. Compact design saves significant under-sink space. Often has a higher water flow rate.
- Cons: More expensive. Requires higher incoming water pressure to work effectively. May need electricity to power a pump for a fast flow.
For most families, a tankless reverse osmosis system offers the best balance of convenience and cost. These systems are commonly installed under sinks connected to water faucets, kitchen faucets, or even laboratory prep stations in home labs or workshops.
Sizing Calculator: Find the Right Reverse Osmosis Tank for Your Home
Choosing the correct tank size is crucial for satisfaction with your RO system. A tank that’s too small will leave you waiting for water, while one that’s too large wastes space and money. Efficient water use is also critical. Based on recommendations from the U.S. Environmental Protection Agency (EPA), right-sizing water systems can help conserve water, reduce waste, and optimize household efficiency—especially in regions facing water scarcity.
Use this simple guide to estimate the right size for your household.
Step 1: Calculate Your Daily Water Needs
First, estimate how many gallons of water your family uses for drinking and cooking each day.
- Number of People in Household: ______
- Average Daily Drinking Water per Person: 0.5 gallons (a common estimate)
- Daily Cooking/Other Use: ~0.5 to 1 gallon total
Calculation: (Number of People × 0.5) + 1 = Total Gallons Needed Per Day
Example: For a family of 4, you would need (4 × 0.5) + 1 = 3 gallons of purified water per day.
Step 2: Understand "Drawdown" Capacity
A key factor is drawdown, which is the actual amount of usable water a tank holds. An RO tank is never completely full of water because the air bladder takes up space.
- A 4-gallon tank typically has a drawdown of 2.5 gallons.
- A 5-gallon tank typically has a drawdown of 3.2 gallons.
- A 10-gallon tank typically has a drawdown of 7 gallons.
Step 3: Match Your Needs to a Tank Size
Based on your daily needs, choose a tank with a drawdown capacity that meets or exceeds your calculation.
| Household Size | Estimated Daily Need | Recommended Tank Size (Total Capacity) |
| 1-2 People | 1.5 - 2 Gallons | 3 or 4 Gallon Tank |
| 3-4 People | 2.5 - 3 Gallons | 4 or 5 Gallon Tank |
| 5+ People | 3.5+ Gallons | 5 Gallon Tank or larger |
| Heavy Use / Ice Maker | 4+ Gallons | 10 Gallon Tank or larger |
Other Factors to Consider:
- Recharge Speed: Your RO system needs time to refill the tank. If you use large amounts of water at once (like filling multiple large pots), a larger tank is better because it gives the system more time to produce water.
- Incoming Water Pressure: Low water pressure can slow the refill rate, making a larger reserve in the tank even more important. Homes with well water often have variable pressure, so a larger tank is a safe bet.
RO Tank Installation & Setup—Step-by-Step
Installing a new or replacement reverse osmosis tank is a straightforward task that most homeowners can do themselves. Here is a general guide.
What to Check Before You Start:
- RO Tank Pressure: Before connecting it, check the air pressure in the empty tank with a low-pressure tire gauge. It should be 5–8 psi. If it’s not, use a bicycle pump on the air valve (usually at the bottom) to adjust it.
- Connections: Ensure you have the correct fittings and tubing. Most tanks use a 1/4-inch connection.
- Shut-Off Valve: Make sure the shut-off valve that supplies water to the RO system is easily accessible.
Installation Steps
- Turn Off the Water: Close the main shut-off valve that feeds your RO system. This is usually a small valve connected to your cold water line. Open the RO faucet to drain any remaining water and release pressure from the system.
- Prepare the Tank: If your tank has an included stand, place it on it. Wrap the threaded connector on top of the tank with 3-4 layers of thread seal tape (Teflon tape) clockwise.
- Attach the Tank Valve: Screw the tank's shut-off valve onto the threaded connector. Hand-tighten it, then give it a final quarter-turn with a wrench. Do not overtighten.
- Connect the Water Line: Push the 1/4-inch water line from the RO system firmly into the quick-connect fitting on the tank valve. Give it a gentle pull to ensure it’s secure.
- Turn the Water Back On: Slowly open the main water supply valve. Check for leaks around the tank valve and tubing connections.
- Let the Tank Fill: It will take 2-4 hours for the new RO tank to fill completely for the first time. Do not use the water during this initial fill.
- Flush the System: After the tank is full (you’ll hear the system stop making water), drain the entire tank by opening the RO faucet. This flushes any sanitizing solution or manufacturing debris from the tank and water filters.
- Refill and Use: Allow the tank to fill a second time. This water is now ready for drinking.
Quick Installation Checklist
[ ] Water supply to RO system is OFF.
[ ] Empty tank air pressure is checked (5-8 psi).
[ ] Threaded connector is wrapped with seal tape.
[ ] Tank valve is securely attached.
[ ] Water line is firmly connected.
[ ] System is checked for leaks after turning water on.
[ ] Tank is filled and flushed completely ONE time before use.
Maintenance & Troubleshooting for Your Reverse Osmosis Tank
Proper maintenance ensures your RO tank lasts for years and continues to deliver clean, great-tasting water. Here are routine care tips and solutions for common problems.
Routine Care Tips
- Annual Pressure Check: Once a year, empty the tank completely. Use a low-pressure gauge to check your RO system tank pressure. It should be between 5–8 psi. If the pressure is too low, how to repressurize my reverse osmosis storage tank? You can re-pressurize your reverse osmosis water storage tank using a simple bicycle pump. This is the single most important maintenance step.
- Filter & Membrane Replacement: Clogged filters are a primary cause of tank issues. Replace your pre-filters and post-filters every 6-12 months and the reverse osmosis filter membrane every 2-3 years. This maintains good water pressure and flow
into the storage tank. - Sanitization: Sanitize your entire RO system, including the tank, annually or whenever you change the membrane. This prevents the growth of bacteria and eliminates odors. Kits are available for this purpose.
Troubleshooting Flowchart: Common Tank Problems
Is your faucet sputtering or is the flow weak? Use this guide to diagnose the issue.
Problem: Low or No Water Flow from Faucet
Is the tank heavy or light?
- Heavy: This means the tank is full of water but isn't dispensing it. The most likely cause is a loss of air pressure.
Solution: Empty the tank, check the air pressure with a gauge, and repressurize it to 5–8 psi. If you add air and water comes out of the air valve, the internal bladder has ruptured and the tank needs to be replaced.
- Light: This means the tank is not filling with water.
Check the Water Supply: Is the valve to your RO system fully open?
Check the Filters: Are your pre-filters or membrane clogged? A clogged reverse osmosis filter or sediment filter will stop the system from making water. Replace them if they are due.
Check for Kinked Lines: Ensure none of the water lines are bent or pinched.
Problem: Sputtering Faucet
- Cause: This usually indicates air in the system or an exhausted tank.
- Solution: The tank is likely empty and needs to refill. If it happens frequently with a full tank, it could signal an air leak at a connection or that the tank is waterlogged and needs to be re-pressurized.
Problem: Bad Taste or Odor
- Cause: Stagnant water or bacteria buildup.
- Solution: If you haven’t used the water in over a week, drain the tank and let it refill with fresh water. If the odor persists, sanitize the entire system and replace the post-filter (carbon filter), which is responsible for the final taste and odor removal.
When & How to Replace a Reverse Osmosis Tank
With proper care, a quality reverse osmosis tank can last 5 to 10 years. However, they do eventually wear out. Knowing the signs of failure can save you from a system that doesn't work when you need it.
Signs Your Reverse Osmosis Tank is Bad
- Constant Low Water Pressure: If you've re-pressurized the tank multiple times but the flow remains weak, the internal bladder may have lost its elasticity and can no longer push the water out of the tank effectively.
- It's "Waterlogged": This is the most common failure. The air bladder ruptures, allowing water to fill the air chamber. The tank will be extremely heavy and will only produce a small amount of water before the flow stops. To check, press the pin on the air valve at the bottom. If water squirts out instead of air, the bladder has failed and the tank must be replaced.
- Water Taste Issues: If you notice a metallic or rubbery taste that doesn't go away after flushing the tank and replacing the filters, the tank's internal liner may be degrading.
- External Rust or Leaks: Visible corrosion or leaks from the tank seams are clear indicators that it's time for a new one.
Step-by-Step Replacement Guide
Replacing a tank is very similar to a new installation.
- Turn Off Water & Drain: Shut off the water supply to the RO system and open the faucet to drain all pressure.
- Disconnect Old Tank: Disconnect the water line from the old tank's valve. Unscrew the valve from the tank.
- Remove Old Tank: Carefully lift the old, likely heavy, tank out from under the sink.
- Install New Tank: Follow the installation steps outlined in Section VI of this guide. Remember to check the pre-charge pressure, use thread seal tape, and flush the new tank completely before use.
Eco-Friendly Disposal
Most municipal recycling programs accept steel for recycling. Before taking your old tank to a recycling center, make sure it is completely empty of water and that the air valve is open to release all pressure.
Advanced Topics for Power Users
For those who want to get the most out of their water filtration setup, here are a few advanced considerations.
High-Capacity Systems and Tank Compatibility
Many homes use refrigerator water filters reverse osmosis systems to supply both ice makers and drinking faucets, a standard RO tank may not be enough. You can connect two or more reverse osmosis accumulator tanks together with a 'T' fitting to increase your total storage capacity. This ensures one appliance's use doesn't drain the entire supply.
Enhancing Water Taste with Remineralization
One common critique of reverse osmosis is that it produces very pure, slightly acidic water, which some people find has a "flat" taste. This is because the RO membrane removes healthy minerals along with contaminants. According to the World Health Organization (WHO), although reverse osmosis removes harmful contaminants, it can also eliminate essential minerals like calcium and magnesium. Prolonged consumption of demineralized water may affect taste and, in some cases, long-term health outcomes.
To solve this, you can add a remineralization filter after the RO tank. As water leaves the tank on its way to the faucet, it passes through this filter, which adds small amounts of calcium, magnesium, and other healthy minerals back into the water. This improves the taste and raises the pH, creating a more pleasant "spring water" flavor.
The Role of Pressure Booster Pumps
A standard RO system needs at least 40 psi of incoming water pressure to operate efficiently. If your home's pressure is below this (common in homes with well water or in some city high-rises), your system will produce water very slowly, waste more water, and may struggle to fill the RO storage tank.
A booster pump is a small electric pump installed on the intake line of the RO system. It increases the incoming water pressure to an optimal level (usually 60-80 psi). This has a dramatic impact on tank performance:
- Fills the Tank Faster: Higher pressure pushes water through the membrane more quickly.
- Improves Water Quality: The system operates at peak efficiency, rejecting more contaminants.
- Reduces Wastewater: An efficient system sends less water down the drain.
If your RO tank is slow to fill, a booster pump could be the solution.
Expert Insights & Unique Data
Water system installers are on the front lines of RO tank performance and failure. We've gathered some of their key observations to provide you with insider tips.
- The #1 Forgotten Task: Installers report that the vast majority of service calls for "low water flow" are resolved by simply re-pressurizing the tank. Homeowners often forget this simple annual check. Setting a yearly calendar reminder can prevent 90% of flow-related issues.
- Sizing Matters for Satisfaction: Experts note that a common customer complaint is the system's inability to keep up with demand. This is almost always a sizing issue. They advise that if you plan to connect an ice maker, you should opt for a tank one size larger than your household calculation suggests. An ice maker's frequent, small draws can keep a smaller tank from ever reaching full capacity.
- Lifespan Reality Check: While tanks can last 10 years, installers find that in real-world conditions with average maintenance, a 5-7 year lifespan is more realistic, especially for steel tanks in humid under-sink environments where the exterior can corrode. Choosing a plastic or composite tank can extend this lifespan.
FAQs
1. What is the life expectancy of a reverse osmosis tank?
The operational life of a reverse osmosis (RO) tank extends between 5 to 10 years based on usage patterns and maintenance practices and water quality conditions. The typical residential RO tank operates through a bladder-style pressure system which uses a butyl rubber diaphragm to divide the water chamber from the air chamber. The bladder material deteriorates naturally as the tank experiences repeated high pressure conditions and continuous high water usage.
The tank's operational duration depends heavily on proper maintenance practices. The recommended annual air pressure check for the tank should maintain 7–8 psi when the tank contains no water. The tank's bladder may rupture and water flow will decrease if the air pressure remains unadjusted.
The tank's durability depends heavily on the quality of the water entering the system. The presence of calcium and magnesium in hard water leads to scale formation which affects both the RO membrane and the tank walls throughout time. The tank lining together with the membrane will degrade when pre-filters fail to remove high chlorine levels which shortens the system's operational lifespan.
Regular filter replacements combined with correct air pressure and proper pre-treatment of feed water enable RO tanks to reach a lifespan of 10 years or more. The lifespan of components becomes shorter when systems face harsh water conditions or receive inadequate maintenance which leads to replacement needs.
2. How do I know if my reverse osmosis tank is bad?
The reliable home supply of purified water requires monitoring the reverse osmosis water tank for signs of malfunction. A malfunctioning reverse osmosis tank becomes evident when the water flow from the faucet becomes substantially lower even after re-pressurizing or replacing the filter cartridge. The tank develops internal problems which manifest as reduced water flow because of liner damage or incorrect pressure settings. The tank shows excessive weight but produces minimal water flow which is a typical problem. The condition known as “water immersion” occurs when the tank fails to dispense water normally because of insufficient air chamber pressure or a damaged internal air bladder. You can check the tank's air valve which exists at the bottom or side of the tank to perform a basic test. A damaged internal air bladder causes water to leak from the valve which indicates a tank malfunction because a functioning tank would never display this behavior. Inspect the tank exterior for any signs of rust together with leaks and corrosion. The presence of these signs represents both aging indicators and safety threats that require immediate replacement of the tank. The reverse osmosis tank requires replacement when it shows symptoms of low water flow or a heavy tank or water leakage from the air valve or external damage. Timely detection of these issues helps avoid system breakdowns while maintaining consistent water quality.
3. What pressure should my RO tank be at?
The standard air pressure for an unoccupied reverse osmosis (RO) tank should be between 5 and 8 psi with 7 psi being the most commonly recommended pressure. The specified pressure range allows the tank to deliver purified water through air compression when it becomes full. A tank with insufficient pressure will produce weak water flow while excessive pressure will prevent proper tank filling which reduces water storage capacity.
First turn off the RO system and drain the tank completely by leaving the faucet open until the water stops flowing. The air valve located at the bottom or side of the tank requires a low-pressure tire gauge to check its pressure. A standard bicycle pump can be used to increase the pressure when necessary adjustments are needed. Not to over-inflate, the bladder inside and water delivery performance will suffer if the tank receives excessive pressure during inflation.
The tank pressure reading becomes invalid when the tank contains water because it produces inaccurate results.
4. What happens if an RO tank has too much pressure?
High air pressure in an empty RO tank between 15 to 20 psi creates excessive resistance which blocks proper tank filling. The tank will store minimal water while feeling abnormally light because of this issue. The faucet delivers brief periods of strong water pressure before the water flow stops completely. The tank's effective capacity decreases because the air chamber pushes back with excessive force when it is overinflated. The tank's normal operation and water storage will return after you release air from its valve until the pressure reaches 5 to 8 psi.
5. How often should I drain my reverse osmosis tank?
It is recommended to drain the reverse osmosis water tank at least once a year, which should be treated as part of routine maintenance. This ensures more accurate pressure checks, prevents wastewater from accumulating inside, and keeps the system running efficiently. Draining the tank once a year is typically done during filter cartridge replacement or when checking the tank's air pressure. Additionally, if you are away for more than a week, it is advisable to drain the water from the tank upon return. Stagnant water can develop a poor taste and may harbor bacteria. Flushing the system and refilling it with fresh water ensures that the water remains fresh and clean.