Why Reverse Osmosis Water Flow is Slow?

If the water coming out of your Reverse Osmosis (RO) faucet seems to be slower than normal, or slower than you think it should be, here are six reasons that can make your under sink RO have slower water production:

1. Clogged RO Membrane Slows Water Flow

If you forget to change reverse osmosis membrane, with time your system will produce less and less water. Reverse osmosis membranes are fragile and can become fouled if not changed often. Trying to fill your tank with a fouled membrane may take 4-6 hours, rather than the usual 2-4 hours. Generally, RO membranes only need to be replaced every 24 months. We suggest setting a calendar reminder to buy a reverse osmosis replacement membrane. 

2. Pressure in Tank Might be Low

Slow water flow rates might be a result of low pressure inside the RO tank. Reverse Osmosis tanks should have pressure of 7 to 8 psi without any water in the tank. To check your pressure, locate the Schrader valve, typically covered by a blue plastic cap, on the side of the tank near the bottom. After removing all the water from the tank, use a pressure gauge to determine the pressure in the tank. If low, add air with a pump until you have 7-8 psi. Be careful to only add a small amount of air at a time, as too much pressure can rupture the air bladder.

3. Ruptured RO Tank Bladder

If you only get about one cup (8 oz) of water out of your RO faucet at normal water pressure, and then the water promptly trickles down to a very small stream, this typically is a sign the air bladder in the storage tank as ruptured. Unfortunately the air bladder cannot be repaired and the only way to resolve the issue is to replace the storage tank. Replacement tanks can be found here. 

4. Clogged  Filters Can Slow RO Water Flow

Replacing your water filter on schedule is crucial to keeping your drinking water clean and delicious. If your 5-stage RO system is producing water slowly, you probably need to change your carbon block, sediment, or GAC polishing filters. In fact, clogged filters are probably the most common reason for reverse osmosis slow water flow to be slow. Filters should be changed annually, unless water conditions and contaminants present require more frequent filter changes (like every six months instead of 12).

5. Kink in Water Line Can Disrupt Flow

Make sure there are not any kinks in the water line, which would slow water production. And while you're inspecting your reverse osmosis drinking water system, double check that the water supply line valve is in the fully open position.

6. Loss of RO Water Pressure

You may have temporary loss of water pressure. An RO system needs a minimum of 40 psi to operate properly, but preferably 60 psi. If all of your household faucets seem to have low water pressure, it may be that your local water utility company is temporarily flowing as lower pressure. Often, higher water pressure will return if you wait a bit. If higher water pressure does not resume, report the issue to your local water utility company.

You might also want to read up on how to properly maintain your reverse osmosis system.

Is Your Reverse Osmosis System Not Producing Water Fast Enough? 

If your reverse osmosis unit seems to be producing less filtered water than it did previously, we outline here a few simple steps to check the current production rate of your RO system. 

Follow these 5 Steps to determine how much water your reverse osmosis drinking water system is producing over a 24-hour period, and some suggestions for increasing the flow rate.

How to Determine Water Flow Rate of Your Reverse Osmosis System

With the water turned on to the reverse osmosis system,

Step 1:  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).

Step 2:  If you have a standard 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 of the system will flow from the faucet.

Step 3:  After there is no more water in the system lines, you may need to wait 1-5 minutes at which time you will/should get a continual fast drip or very slow flow from the faucet.  (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 storage 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.

If you want an hourly water production rate, simply divide the number by 24. 

Example: Within 1 minute your system is 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

After you understand exactly how much water your RO system is producing, you can better asses the situation. For example, if you've determined that the RO system's flow rate has decreased, you can now work to figure out the cause and find a solution. 

Again, a decreased flow rate may be caused by clogged filters or a fouled membrane that simply need to be replaced. To troubleshoot a variety of issues relating to your reverse osmosis system, you may find this page helpful as we list symptoms, probable causes and the recommended solution.

Additional RO Slow Water Flow Troubleshooting Assistance

You might want to consult our troubleshooting guide or call a water treatment specialist in your area for additional assistance. For products purchased through espwaterproducts.com, customer support is available Monday through Friday 8 am to 5 pm (Central time) at 877-377-9876. Have your customer or invoice number ready.

NOTE: "filter bundles" are a convenient way to take care of annual filter replacements. These annual replacement kits include everything you need for annual filter replacements, and often save you time and money. Find your filter bundle by first identifying your RO system brand/model.