Reverse Osmosis Tank Not Filling?

RO tank not filling

4 Reasons Your RO Tank is Not Filling Up

If your reverse osmosis storage tank is not filling up (or filling very slowly), we'll help you troubleshoot the issue. From examining your household water pressure, to clogged filters or even low tank pressure, we'll do our best to help your find the answer.

RO tank not filling due to low water pressure

Household Water Pressure May Be Low

To operate a Reverse Osmosis (RO) drinking water system, the ideal household water pressure is 60 psi. But most RO systems will operate properly if pressure is between 40 and 80 psi. When household water pressure is low (near or below 40 psi), water cannot push through the RO membranes to produce filtered water. A booster pump can increase the water pressure going into the RO system.

RO tank not filling due to clogged filters that need replacing

RO Filters May Need Replacing

Clogged filters are often the main culprit when an RO tank is filling slowly. RO water filters should generally be replaced every 12 months and the reverse osmosis membrane every 24 months. When filters can no longer absorb contaminants, they become fouled or clogged. This can slow the filtered water production rate to just a trickle. Check out more details: Why You May Have Slow Flow Rates From Your RO System.

RO tank not filling due to low tank bladder pressure

RO Tank Bladder May Have Ruptured

The ideal tank pressure is 8 pounds per square inch. When pressure in the tank is low, water cannot be delivered to the faucet. If tank pressure is high, the water coming from the filters won't enter the RO holding tank. To pressurize an RO tank, drain all water from the tank and then use a bicycle pump to bring pressure to 7-9 psi. RO pressure tanks can wear out with time, so if the tank bladder is ruptured, the tank will need to be replaced. RO Troubleshooting Guide.

RO tank not filling because of system low gpd capability

RO System May Have Low GPD Rate

RO systems are rated on their "gallons per day" (GPD) production rate. The RO system's GPD will impact how quickly water will fill the storage tank. This means that a 100 GPD system will replenish the water storage tank twice as fast as a 50 GPD RO system. If an RO system is not producing at capacity, follow the steps below to determine how much water the RO system is producing in a 24-hour period.

RO Troubleshooting Guide

Discover effective solutions to common reverse osmosis (RO) water filtration issues. Our troubleshooting guide provides maitenance tips and answers your RO system questions.

How Long Does It Take to Fill an RO Storage Tank?

If your Reverse Osmosis water tank isn't filling, and you are wondering how long it normally takes to fill an RO tank, the short answer is it typically takes 2 to 4 hours to fill a standard reverse osmosis holding tank (2.8 gallons or 10.6 L).

Because the reverse osmosis filtering process takes time, storage tanks are a necessary component with any RO system. Without an RO holding tank, you would have to wait 5-10 minutes just to fill a glass of water. With an RO storage tank, you can quickly fill your glass, pot, or water bottle.

It typically takes 2-4 hours to fill an empty RO pressure tank

Millions of Households Enjoy Delicious Drinking Water from RO Systems

How to Determine Water Flow Rate of Your RO Unit

1. Prep RO System

First, make sure the incoming water line to the Reverse Osmosis system is turned "ON". Then, turn the ball valve on top of the reverse osmosis storage tank to the "OFF" position (generally a 1/4 of a turn).

2. Open Faucet to "Flow" Position

On your reverse osmosis faucet, flip the handle to the "up" position, so the faucet is now locked into a continually open/flow position. At this time any water in the lines will drain.

3. Drain Tank

After there is no more water in the system lines, wait about 5 minutes to make sure all water has drained. (NOTE: If you get no flow from the reverse osmosis faucet, the system is not producing water).

This flow rate represents the flow rate if the system is producing water and the rate that the reverse osmosis storage tank would be filling if the valve on the reverse osmosis pressure tank was in the "open" position.

4. Measure Drips

Once you have a continual drip or slow flow from the faucet, using a measuring cup, measure how much water drips/flows from the reverse osmosis faucet into the measuring cup for 60 seconds.

5. Do the Math

Now it's time to do the math!

    • Take the number of ounces your RO system produced in one minute.
    • Multiple this number by 1440, which is the number of minutes in a day.
    • Divide this number by 128 which is the number of ounces in a gallon.

This number is the amount of water your RO system is producing over a 24-hour period.

To Determine Hourly RO Production Rate:

If you want to know the hourly water production rate of your reverse osmosis system, simply divide the number (daily rate) you got above by 24.

Example: Within 1 minute your system produces 4 ounces per minute. 4 x 1440 (minutes in day) = 5760 (ounces) divide by 128 (ounces in a gallon) = 45 gallons per day. Divide by 24 (hours in day) = 1.875 gallons per hour

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Top-Selling RO Storage Tank

The PAE 4.4 Gallon RO storage tank is a top-selling pressure tank because of its durable construction and reliability. Built-in sealed brass air valves and o-ring sealed air valve caps ensure leak-free air chamber.

  • Patented stainless steel water connection
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  • Total volume = 4.4 gallons
  • Holding capacity = 2.8 gallons


How to Test Home Water Pressure

You can purchase an inexpensive water pressure gauge at your local home improvement store. Make sure water is turned off both inside and outside of the house as any moving water can cause a low water reading. This includes shutting off lawn sprinklers, dishwasher, washing machine, etc.

From there, follow the package directions on the pressure gauge. Be sure to test from the hose bib closest to the water meter, if on city water. If on well water, test at the hose bib closest to your well holding tank.

How a Reverse Osmosis Tank Works

An RO storage tank uses pressurized air to push filtered water to your faucet. Pressure in the tank is important because an RO drinking water system doesn't use electricity to deliver water. When water from the RO system goes into the tank, it begins to compress the air in the air chamber which then pushes water out to your RO faucet.

What is the Lifespan of an RO Pressure Tank?

RO pressure tanks typically last 7-10 years. You do not need to replace the tank until the air bladder inside goes bad and is no longer able to push the water out of the tank. When this happens, typically you’ll get approximately one cup of water at normal pressure before the water pressure immediately drops to a very small stream of water, but the tank still feels heavy and full of water. This indicates the tank is empty and needs to be replaced. You do not need to replace storage the tank until the tank goes bad.

Why Does a Reverse Osmosis Tank Gurgle and Make Noise?

Once your storage tank is filling up again with filtered water, you may hear a gurgling noise. That noise is common, especially with new installations. This is caused by air in the tank and indicates the system is now producing water and replacing air in the pressure tank with water. The noise should stop after a few days.

Another reason you may be hearing noise could be due to the type of faucet you have connected to your RO system. An air-gap faucet makes more noise than a non-air-gap faucet. A little noise is common with "air-gap" faucets "gurgling" noises are typically heard as the contaminated water goes to the drain line.

If you ever hear "hissing" noises, you should immediately call your local water treatment professional. Hissing noises may mean there is a problem with water pressure, the air gap faucet, or a leak. More tips available in our RO Troubleshooting Guide.

Top-Selling Reverse Osmosis Drinking Water Systems

Microline TFC-400-ESP RO System 50 GPD TFC-400-ESP

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AXEON Solo I All-In-One 4-Stage 50 GPD RO System (211470)

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GRO 1:1 RO High Efficiency 75 GPD Drinking Water System (GRO-75GPD)

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  • Proven, High-Quality System
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  • Designer Chrome Faucet
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  • High-Flow 3/8" Tubing to Faucet
  • High-Flow 3/8" Tubing to Faucet
  • 4-Stages of Filtration
  • 4-Stages of Filtration
  • 4-Stages of Filtration
  • Compact 3.2 Gallon Storage Tank
  • Standard 4.4 Gallon Storage Tank
  • Standard 4.4 Gallon Storage Tank
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  • Airgap Faucet Connection
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  • 50 Gallons Per Day
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