Reverse Osmosis Tank Not Filling?


Why is My Reverse Osmosis Tank Not Filling Up?

If your reverse osmosis tank is not filling up (or filling very slowly), here are four ways to troubleshoot this issue.

  1. Household Water Pressure May Be Low: The ideal water pressure for operating most Reverse Osmosis (RO) under sink drinking water systems is 60 psi. Though, most RO systems should operate properly if water pressure is between 40 and 80 psi. When your household water pressure is low (near or below 40 psi), water cannot be pushed through the RO membranes to produce filtered water. If problems persist, you may need to add a booster pump to your RO system to increase the incoming water pressure to the RO system. We recommend checking your home water pressure a few times a year to address any issues. How to test home water pressure>>
  2. Filters May Need Replacing: 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 and become fouled or clogged, the flow rate on your reverse osmosis system can slow to just a trickle. Clogged filters are often the main culprit when an RO tank is filling slowly. Check out more details: Why You May Have Slow Flow Rates From Your RO System.
  3. Tank Bladder May Have Ruptured or Have Low Pressure: The pressure of an empty RO tank should be 7-9 pounds per square inch. When pressure in the tank is low, water cannot be delivered to the faucet. If tank pressure is too high, then water coming from the filters won't enter the RO holding tank. The ideal tank pressure is 8 psi. You can attempt to re-pressurize your RO tank with a bicycle pump, but be sure to drain all of the water in the tank first. Be aware that RO pressure tanks wear out with time. If your tank bladder is ruptured or damaged, then you will need to replace the tank.  More tips available in our RO Troubleshooting Guide.
  4. RO System May Have a Low Flow Rate: The type of RO system you have will impact how quickly water will fill your water storage tank. The Microline TFC-400-ESP RO System produces 50 gallons of water per day. If you suspect your system is not producing at capacity, Below we provide steps to determine how much water your RO system is actually producing in a 24-hour period.


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.

How Long Does it Take to Fill a Reverse Osmosis Storage Tank?

If your Reverse Osmosis water tank isn't filling, and you're 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.

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.

How to Determine Water Flow Rate of Your Reverse Osmosis System

Step 1: Make sure the incoming water line to the RO system is turned "ON" and turn the ball valve on top of the reverse osmosis storage tank to the "OFF" position (generally a 1/4 of a turn).

Step 2: 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.

Step 3: 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 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.

Step 4: 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.

Step 5: 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.

How to Determine Hourly RO Production Rate

If you want to know the hourly water production rate or your reverse osmosis system, simply divide the number 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

Why Does My RO Tank Make Noise

Once your storage tank is filling up again with filtered water, you may hear noise. That noise below the sink simply indicates the system is now producing more water and refilling the storage tank.

Or it could be an air-gap faucet noise if you have an air gap faucet with your RO system. 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.

Replacement Reverse Osmosis Tanks