Reverse osmosis tank not filling – what are the solutions

A common problem for any home RO system is that the reverse osmosis tank might not be filling. In this article, I shall discuss what are some common causes and recommend solutions you can deploy to solve the problem.


#1: Low air pressure in RO tank

The most common reason for reverse osmosis tank not filling is due to insufficient air pressure in the storage tank. The right pressure should be around 5-7 psi. If the air pressure in your storage tank is not around that range, then water will not fill smoothly.

You can measure air pressure via a low air pressure gauge. If the numbers are below what is needed, then you need to pressurize the storage tank. However, if you find that the tank is not holding the air pressure or there is air leak in the vale, then it is time to replace the storage tank.

If you need recommendation for reverse osmosis tank replacement, may I humbly suggest this unit from PA-E.

reverse osmosis tank replacementThis 4 galleon RO tank has receive lots of positive reviews. The good thing about this tank is that it is already pressurized at the optimal pressure of 5-7 psi so you can use it straight out of the box.  It is a standard sizing as well so you can pretty much use it for any kind of reverse osmosis brand.

Installing this thing is pretty easy. You simply swap out your current storage tank and put this in its place. The connections to the rest of the system is fairly standard so it just unplugging them from the old tank and plugging them into the new one.

However, do note that this unit does not include a ball vale. If you want the option to turn the thing on and off then it is advisable for you to buy a ball vale together with this storage tank.

When you first install the tank, make sure to fill and drain it first. This is because there might be oil that seep into the water during the installation so it is good to discharge the first batch of water that flows into the storage tank.

Overall, the PA-E reverse osmosis tank is a great replacement tank when you find that your current one is not holding its pressure well.


#2: Low water pressure

Another possible reason for your reverse osmosis tank not filling can be due to the low water pressure. This will not be the cause if you have no such problem initially. However, if you are using a RO for the first time and find that your tank is not filling, this is likely to be the cause. Your home’s water pressure is not strong enough to pump the water through the RO system, thus resulting in your tank not filling up. The easiest solution is to buy a booster pump to increase the water pressure of your home.


#3: Clogged filters

If you have not change your filters for a period of time, a clogged filter might be the explanation for why your tank is not filling. Simply check your filters to access if they are ok. If they are clogged, just replace them and your water flow should be back to normal.


#4: Faulty tank bladder

Every RO storage tank comes with a bladder that is pressurized as the tank is filled. It will then use the pressure to force the water out when needed. If your tank bladder is faulty then it might result in the tank not filling up.


#5: Check the vale settings

Again, this only applies to first timers. Sometimes the problem can be due to a simple oversight like not turning the vale to the right setting. If you have set it to “drain open”, then the water will simply pass through the tank without it being stored.



There are many reason why a reverse osmosis tank is not filling up. Hopefully, this list of potential causes can help you resolve your problems. If you have other comments, please feel free to ask them in the comments.

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