This page may contain affiliate links. If you buy a product or service through such a link we earn a commission at no extra cost to you. Learn more.
RO storage tanks require regular cleaning and sanitizing to prevent biofilm buildup from contaminating your drinking water. Part of the cleaning/sanitizing process requires draining the tank until it’s completely empty.
Another reason you may need to drain your RO storage tank is to repressurize it if air has seeped out of it over time.
Draining a reverse osmosis tank is straightforward, and only requires a few steps to complete properly. Let’s take a look at how to drain your RO tank so that it’s fully empty.
Draining an RO tank is a fairly simple process, but it can get messy so it’s best to complete the process outdoors or in a bathtub. Here is how:
Disconnect the tank from the RO system.
Open the tank valve.
Connect a pump or compressor to the tank’s air valve.
Pump air into the tank until it’s completely empty. Don’t go too fast in order to not rupture the plastic bladder.
How to Drain a Reverse Osmosis Tank So That It’s Fully Empty
So, how do you drain a reverse osmosis tank?
The first step to draining a reverse osmosis tank is shutting off the feed water supply to the RO system.
Next, close the storage tank valve on top of the tank.
Disconnect the storage tank from the rest of the RO system. To avoid making a mess, consider taking the tank outside or in your bathtub.
Open the tank valve on top of the tank. Water should shoot out of the valve initially, and then slow down to a trickle after a while.
When the water stops flowing out of the valve you’ll need to use pressure to remove the rest. There is still a significant amount of water left in the tank at this point. Use a bicycle pump or air compressor attached to the pressure valve to pump out whatever water is left inside.
At this point the tank is empty, but you may need to repressurize the tank if you’ve been having issues with low pressure. When done, reconnect the tank to your RO system. Open the tank valve and feed water valve and allow the system to refill.
Additional Tips for Draining RO Pressure Tanks
To repressurize the tank once it’s fully emptied, use a bicycle pump or air compressor to add pressure to the tank until it reaches 6 to 8 psi. You can use a regular tire pressure gauge to check the pressure as you go. Be careful not to over-pressurize.
What’s a Reverse Osmosis Tank and How Does It Work?
RO systems use storage tanks to keep enough water on tap to fulfill your needs at all times. Because RO systems filter water at a slow rate, storage tanks are necessary to keep filtered water on hand whenever you need it.
These storage tanks are pressurized to avoid the need for a booster pump. Inside the pressurized storage tank is both an air chamber and a water chamber separated by a bladder. When the water chamber fills up, the air chamber compresses and increases in pressure.
This air pressure is needed to push the water up to the RO faucet when it’s opened. Without the air pressure, the water could enter the storage tank, but not leave it without the need for a pump.
RO tanks come in different sizes, with 4 gallons being common for most under sink units. In these tanks, the water chamber rests above the air chamber. Larger 10+ gallon tanks are built the opposite way, with the water chamber on the bottom.
Why Do You Need One?
RO systems filter water at a fairly slow rate, so without a storage tank you would need to wait a significant amount of time every time you filled a glass of water. The storage tank keeps enough water on hand to deliver filtered water whenever you need it – so you don’t need to sit around waiting for the filter to work.
Another function of a pressurized storage tank is maintaining pressure throughout the entire reverse osmosis system. The system halts the filtration process when the pressure in the tank reaches a pre-set level. This regulates the water production – and ensures you don’t produce excessive wastewater.
How Long Does It Take to Fill an Empty RO Water Storage Tank?
RO storage tanks take longer than one might think to fill up. This is a function of the speed of the filtration process. For an average 4-gallon storage tank, you’re looking at 2 to 4+ hours to fill completely.
Keep in mind that the actual tank capacity will be less than the stated number. The 4-gallon figure refers to the total volume of the tank, which includes the air chamber. So, for a 4-gallon tank, you’re looking at between 2 and 3 gallons of actual water storage capacity.
The actual speed at which your tank will fill also depends on several other factors like your feed water pressure, the water temperature, the RO system capacity, and whether or not any of the filters are clogged.
If you have any questions about how to empty a reverse osmosis tank 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.
Learn more about Gene and the rest of the BOS Team.
Information provided on BOS is for educational purposes only. The products and services we review may not be right for your individual circumstances.
We adhere to strict editorial guidelines. Rest assured, the opinions expressed have not been provided, reviewed, or otherwise endorsed by our partners – they are unbiased, independent, and the author’s alone. Our licensed experts fact-check all content for accuracy. It is accurate as of the date posted and to the best of our knowledge.
Leave a Comment:
John says
May 25, 2023
I have been filling 1 gallon jugs (two at a time) at a friend’s house when I visit with them twice a week. This nearly drains the tanks so I always stop after 1.5 gallons in case someone wants a glass of water during our visit, they wouldn’t have to wait. Then before leaving, I would top off the rest of my half full gallon after the RO system had a chance to refill the tank. I would leave with two full gallons and my friends still had water to drink before bed. I never wanted to leave them dry, so I was always strategic in filling my two gallons worth during my visit. However, they left town for a month recently and they still allowed me to enter their house for water. So now, I would have no concern about leaving them without water since they were away. I therefore let the RO system go as far as it could to fill two gallons. The final half gallon was painfully slow, so I would watch a little TV while I waited and by the end it was practically dripping. Could this much drainage damage their system? A week or so after returning from their visit, their system developed a leak above counter and their repair rep was trying to blame it on me stating “this unit is not made for commercial usage!” My first thought when I heard this was “what are you supposed to do if you want to boil water for pasta and serve water to your guests at dinner? Two gallons, a couple times a week is NOT commercial usage!” What are your thoughts? Do you think I was the cause of the leak?
Hi John,
Where was the leak exactly? You are right, using 2 gallons at a time is not commercial use and any RO system should be able to handle that with ease.
