RO membrane GPD rating refers to the amount of water a reverse osmosis membrane can produce within 24 hours under ideal conditions (60 psi feed water pressure and 77 °F water temperature).
The most common GPD ratings for tank-based RO membrane systems are 50, 75, and 100 GPD.
50, 75, 100 – What’s the Meaning of RO Membrane GPD Ratings?
So, what is GPD in an RO membrane?
GPD stands for “gallons per day”. It is a rating for how much water a reverse osmosis membrane can produce within 24 hours of continuous use. A 100 GPD rating, for example, means that your RO membrane can provide up to 100 gallons of water per day.
However, RO membrane GPD ratings are ideal values that are measured under optimum lab conditions. Usually, the industry standard for such measurements is 60 psi for water pressure, and a water temperature of 77 °F. These standard conditions may not be present in your home. So, if your water is colder than the standard temperature or you have a lower feed pressure, your reverse osmosis system/membrane will produce fewer gallons of water.
Factors like water contamination level and membrane age/condition can also contribute to a reduced GPD. As a result, the average RO system has a production rate of around 50-80% of its original GPD rating. So, a system with a GPD rating of 50 may only process 30 gallons per day.
And finally, it’s important to know that not all vendors calculate the GPD ratings according to industrial standards. Some RO brands claim their systems have a rating of 100 GPD at 100 psi — which is a very impractical input water pressure! So ensure you check these facts before you buy a reverse osmosis system based on the GPD rating of an RO membrane.
Is Higher Reverse Osmosis Membrane GPD Better?
Having an RO membrane with a high GPD has its benefits, but it might not be for you. The ideal GPD rating for you depends on your water needs.
If you have a big household, you’d need an RO system with a higher GPD rating since it can process more water.
However, if you don’t use as much water, it’s not always useful to go for a high GPD unit. For instance, getting a 100 GPD membrane when you use no more than a few gallons of purified water a day may not be a worthy investment. The only real advantage here is that you don’t need to wait too long in case your reverse osmosis storage tank ever runs dry (higher GPD also means faster flow) – which it shouldn’t.
So don’t be too focused on impressive production rates — higher GPD systems have their disadvantages. For example, they tend to have a shorter membrane lifespan. Also, RO membranes self-clean during the filtering process. And since membranes with a lower GPD rating work slower, they have more time to clean while processing water, unlike higher GPD systems which process large volumes of water quickly.
Another downside to higher GPD systems is that they have lower salt rejection rates, which means they don’t filter out as many contaminants as a lower GPD unit. So a 50 GPD RO membrane may have a 99% rejection rate, while a 75 GPD membrane would have 98%, and a 100 GPD membrane would have a 97% rejection rate.
The contaminant reduction rate decreases as the GPD rate increases.
What RO Membrane GPD Rating/Size Do I Need?
We recommend a 50 GPD-rated reverse osmosis system for normal home use. 50 GPD rating might translate to 35 GPD in real life all factors considered, which is enough for most households.
However, if a higher GPD system serves you best, go for it. Higher GPD units don’t cost a lot more than the lower ones.
They also have an adequate production rate to cover up for cold winter months when there’s a drop in water temperature, and when the membrane draws close to the end of its lifespan (average 2-5 years).
A popular alternative to 50 GPD is 75 GPD. It has a good rejection rate (98-99%) and will produce up to 1.5-2 gallons of water per hour.
How Can You Increase the GPD Capacity of Your RO Membrane?
You can’t change the GPD capacity of your existing RO membrane, but you can increase feed water pressure (using a pump) or water temperature.
Alternatively, upgrade to a higher-capacity membrane with a matching flow restrictor. If the high-capacity membrane isn’t matched to the flow restrictor, there’ll be a balance upset between filtered water and wastewater, resulting in excess wastewater and premature membrane fouling. Once you’ve replaced your membrane and restrictor, you can enjoy increased GPD and faster water production.
If you have any questions about RO membrane GPD ratings please don’t hesitate to leave a comment below!
About the Author Gene Fitzgerald
Gene Fitzgerald is one of the founders of BOS and currently head of content creation. She has 8+ years of experience as a water treatment specialist under her belt making her our senior scientist. Outside of BOS, Gene loves reading books on philosophy & social issues, making music, and hiking.
Learn more about Gene and the rest of the BOS Team.
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Leave a Comment:
sam says
March 10, 2024
Hi – I have a newer RO filter system that uses BW60-1812-75 filter membranes (75 gal capacity). It replaced an older RO system, and I still have a couple TW30-1812-50 filter membranes (50 gal capacity). Can I use the 50 gpd membrane filters in my newer RO filter system, just to use them up? I won’t if I need to change the drain line flow restrictor.
