GPD in Reverse Osmosis – What Does It Mean? Learn Here!
Written by: Alexandra Uta // Last Updated: Jun 16, 2023
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There are a lot of abbreviations in the world of reverse osmosis water filtration, from TDS to RO to today’s focus, GPD.
If you have been looking into reverse osmosis for even a little while, I’m sure you have seen it. But what does it mean?
Today we will discuss GPD ratings and what to look out for when you are purchasing your reverse osmosis system.
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Key Takeaways
- GPD in reverse osmosis stands for gallons per day. It is a measure of how much filtered water your RO membrane can produce in a 24-hour time period. The higher the GPD, the more water your system can filter.
What Is GPD in Reverse Osmosis and What Does It Mean?
So, what is GPD in reverse osmosis and what does it mean?
Firstly, GPD stands for ‘gallons per day’, and it is a measure of how much water an RO membrane can produce within 24 hours. For example, if your GPD says 200, then your reverse osmosis membrane can filter 200 gallons of water per day.
The rating is created in a lab using optimal conditions for said membrane, which means perfect feed water pressure (60 psi) and perfect water temperature (77 degrees). As such, your actual GPD may be lower depending on your feed water conditions.
The basic premise is that if your house’s water consumption is low, it may be possible to buy a lower-capacity RO system with a lower GPD rating. On the other hand, if more people are living in the house or if you use a lot of water, then it might be better to buy an RO system with a higher GPD rating.
What Is a Good GPD Rating for a Reverse Osmosis System?
Depending on the feed water conditions and your membrane age, it is a good idea to reduce the GPD rating of your RO system by 25% to 50% of the original number. So if a manufacturer states a GPD rating of 75, what you might actually get is 37.5 to 56 gallons per day.
Common GPD ratings are 50, 75, and 100.
Is Higher GPD Better?
If you have many people in your household, all using filtered water, then yes, a higher GPD is better as the reverse osmosis system can process more filtered water and means you are less likely to run out of it, especially at peak times.
However, let us say it is just one or two people in the house, and the RO system is used for filling up water bottles just a couple of times a day. In that case, it is not better to have a system with too high of a GPD, as it probably takes up too much room and is a more expensive initial investment for not many positives. Plus, high GPD systems may have shorter membrane lives as they are filtering more water.
There may also be a downside when it comes to the salt rejection rate. Sometimes, higher GPD RO membranes have lower salt rejection rates and filter out slightly fewer contaminants.
What GPD Rating Do I Need?
There is no specific GPD for any household, as it depends on your water needs.
A 50 GPD system is usually ample for the average household, even if age and other factors mean you only get 35 GPD out of it. The best way would be to estimate, as a household, how many gallons of water per day you actually need and go from there.
Factors That Affect RO Membrane Flow Rates
There are several factors that may affect your reverse osmosis membrane flow rates and, therefore, mess with your GPD rating, such as:
- Filters and membranes that are too old: Both filters and membranes in your RO system can become clogged over time with debris, which will lead to a drop in water pressure and less water being pushed through the system. It is essential to change your filters on time. Usually, the carbon and sediment pre-filters every 6 to 12 months, carbon post-filters every 1 to 2 years, and reverse osmosis membranes every 2 to 5 years.
- Clogged or bent tubes: Kinks in your water lines prevent water from flowing effectively through your reverse osmosis filter system and may lower the GPD output. Inspect your system’s lines for kinks and smooth them out by hand. Clogging in the water lines is a little more complex, and they will have to be detached from the system and cleaned manually.
- An overpressurized RO storage tank: If your RO system has a storage tank, the ideal pressure for this tank should be between 6 and 8 psi (when empty). If the levels are above this, it will need to be recalibrated.
- Low home water pressure: Ideally, an RO system works best with home water pressure at 60 psi. Anything below 40 psi will trigger poor performance and a low GPD rate. If your home water pressure is too low for your RO system, you may want to install a booster pump.
- Feed water temperature: Colder water decreases its flow rate through the RO membrane, while a high temperature increases flow. For every °F drop in water temperature, the product flow rate goes down by around 3% and vice versa.
If you have any thoughts about the question, what is GPD in reverse osmosis, please don’t hesitate to leave a comment below!
About the Author Alexandra Uta
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