Reverse Osmosis Membrane Sizing & Upgrade. Inline Polishing Filter Sizing

How to identify the membrane capacity in your Reverse Osmosis RO water filter system and instructions on how to upgrade to a higher capacity Reverse Osmosis RO Membrane.
Replacement Filters Reverse Osmosis RO Membranes, Pumps, Testing Supplies

We Ship To United States and Territories Only.

Shop By Category
Home Page
Search Our Site
Replacement Water Filters
Reverse Osmosis Systems
Reverse Osmosis Membranes
Components & Fittings
Reverse Osmosis RO Holding Tanks
Installation Supplies
Reverse Osmosis Accessories
UV Systems & Lamps
Water Testing Supplies
Contact Us
Sales & Return Policy
Instructional Videos
Reverse Osmosis Troubleshooting Guide
RO Membrane Identification and How To Upgrade
Filter Change Instructions
Manuals & Downloads
Read What Our Customers Have To Say About!
We Accept:
American Express Card
Visa Card


Reverse Osmosis Membrane Sizing & Upgrade. Inline Polishing Filter Sizing

This Guide is intended for customers who have a Standard type Reverse Osmosis System like the one pictured here.

If you have a proprietary system such as Hydrotech, Microline, etc., the basic way to size your membrane and how to upgrade apply, it's just the Drain Flow Restrictor you use is different from the one we describe here. 

Some Reverse Osmosis Systems are available with different capacity RO Membranes and we are often asked by customers "Which membrane does my system use?" and "How do I upgrade to a higher capacity membrane?". On this page we explain the mysteries of the RO Membrane and how you can quickly determine which membrane your system currently uses.

"Which Membrane Does My System Use?"

Many times, the membrane type and capacity are written on the membrane housing itself. 

Type of Membrane
Membranes come in two types, CTA (Cellulose Tri-Acetate) and TFC (Thin Film Composite) sometimes labeled as TFM (Thin Film Membrane). CTA Membranes can tolerate chlorine and TFC Membranes cannot tolerate chlorine. TFC Membranes are more efficient and are the standard type used in today's RO Systems, although systems using CTA membranes are still being manufactured. 

CTA membranes are usually have a capacity of 16 GPD (Gallons Per Day) or less.

TFC (TFM) membranes for residential use are now available at up to 150 GPD.

If your system does not have a label which tells you which type membrane you have, you may have to remove the membrane and look on the label.

Membrane Capacity
Most RO Systems list, on the membrane housing, the capacity of the membrane in GPD (Gallons Per Day). Of course, this makes it easy to find the replacement but if you're reading this, your system most likely does not tell you the capacity. 

Why is this important? To operate efficiently, RO Membranes are matched to the proper size Drain Flow Restrictor. The RO Membrane and Drain Flow Restrictor must be matched to keep the proper balance between waste water and pure water. Mismatching can either cause excessive waste to the drain or premature membrane fouling. 

There are two ways to determine the membrane capacity of your system. One is to remove the membrane from the RO housing and look at the label. The label should tell you the membrane Type and Capacity.

The other is to look at the membrane Drain Flow Restrictor. Most standard RO Systems use an inline Drain Flow Restrictor like the one pictured here. Although not shown in this picture, the Drain Flow Restrictor has a number on it such as 150, 200, 250, etc.

As the Drain Flow Restrictor is sized to the Membrane Capacity, all you need to do is match this number to the chart and you will know the capacity of the membrane your system is currently using.
Number On Flow Restrictor Membrane Capacity
150 16-18 GPD
200-250 24 GPD
300-350 36 GPD
400-500 50 GPD
600-750 75 GPD
800-1000 100 GPD
1200 150 GPD

How Do I Upgrade To A Higher Capacity Membrane?

This is the easy part. As we mentioned, the RO Membrane and Drain Flow Restrictor are matched. To upgrade to a higher capacity membrane, all you need to do is make sure you also replace the Drain Flow Restrictor to match the new membrane. 

Sizing The Inline Polishing Filter and Tubing

Inline Polishing Filters are available in two configurations. One is with Female Pipe Thread (FPT) and the other is Quick Connect Fittings. 

In this picture, the filter on the Left has FPT fittings (The Blue Cap is a plug to keep debris out of the filter). With this type of filter, you have a fitting that screws into this filter and the tubing connects to this fitting.

The filter on the Right has Quick Connect fittings. With this type, the tubing is simply "Pushed In" to the filter and is held in place by the Quick Connect Collar.

If your inline polishing filter has FPT threaded fittings, the most common size is 1/4". 

As you can see in this picture, 1/4" FPT is approximately 1/2" wide if measured with a tape measure.

Tubing Size

The tubing on the LEFT is 1/4" tubing. The tubing on the RIGHT is 3/8" tubing. Most times, the tubing is labeled with the size. Just look on the tubing and it will have writing on it telling you the type and size.

Holding Tank Air Pressure Gauge
Reverse Osmosis Hiolding Tank Pressure Gauge
The number one reason for low water flow from a reverse osmosis system is low air pressure in the holding tank.

With this holding tank air pressure gauge you can easily check and maintain the holding tank air pressure to the required 8 PSI of air pressure to get your system up and running at its' peak efficiency.

Specially designed for use with low air pressure applications, this Holding Tank Air Pressure Gauge is a must for Reverse Osmosis Systems maintenance.OUT OF STOCK. 


TDS Meter
TDS-EZ Total Dissolved Solids TDS Meter
HM Digital, Inc., TDS-EZ Total Dissolved Solids Meter

The HM Digital EZ TDS meter is a must for reverse osmosis (RO) filter and membrane monitoring. Know when to change your pre-RO filters to extend the life of the RO membrane. Designed for home use, this pocket TDS meter comes with a 2 year limited manufacturer's warranty.Designed for the long haul, this compact TDS (Total Dissolved Solids) meter has been manufactured with a tough housing and large, easy to read LCD screen. It sports a measurment range of 0 to 9990 parts-per-million. Flip it over and the back side sports a handy color coded chart which classifies the water you are testing.The TDS-EZ is perfect for monitoring your reverse osmosis (RO) output water. Take the guess-work out of knowing when to change your filters! 



USPS Shipping to United States is never more than $13.60!

Stock Up And Save!

Using Our Shopping Cart Is Simple and Easy.

You do not have to add one item at a time.

Simply add a Quantity of each item you need in the Quantity Box and Click on any "Add To My Shopping Cart Button". 

All items selected will be added to your Cart at once!

To View items in your Cart and/or make changes, please click here:
View/Modify Shopping Cart!

If you have items in your Cart and are ready to Checkout, please click here:
Proceed To Checkout!

RO Tubing
Water Softener Tubing
Ball Valves
Holding Tanks
RO Membrane Housings
Filter Wrenches
Auto Shut Off Valves
Flow Restrictors
Check Valves
Filter Clips
Feed Valve & Adaptors
Drain Clamps
RO & Softener Drain Line Adaptors
Air Gaps
Pressure Regulators
Relief Valves
Hammer Arrestors
Pressure Limiting Valves
Reverse Osmosis Membranes
Replacement Water Filters supports Made In The U.S.A.!
Where possible, we offer USA made products. Look for this flag:


*The replacement filters and membranes advertised on this site are not manufactured by the companies that manufacture the underlying water treatment equipment unless so noted.  Our use of registered trademarks, such as Culligan®, Kiss®, Premier Manufactured Systems® and others, is only for purposes of identifying compatible replacement filters and membranes, and does not suggest any association, sponsorship or endorsement of our our products by the manufacturers of the underlying equipment. "COMPATIBLE" Legal Disclaimer
COPYRIGHT is a trademark of Purewater 4U of Las Vegas, Inc. All other products mentioned are registered trademarks or trademarks of their respective companies. Proprietary contents contained herein are the sole property of and Purewater 4U of Las Vegas, Inc. and may not be reprinted, reproduced or transmitted in any form without written permission. Purewater 4U of Las Vegas, Inc., grants permission to electronically copy and to print hard copy portions of this site for the sole purpose of placing an order with or through, or using this site as a shopping resource. Any other use of materials on this site, including reproduction for purposes other than those noted above, modification, distribution, or republication, without prior written permission from Purewater 4U of Las Vegas, Inc. is strictly prohibited. Copyright © 1998 - 2011 Purewater 4U of Las Vegas, Inc. Las Vegas, NV, USA. All rights reserved.