What is GPD in Water Filtration? What Does it Stand For?

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If you’re shopping for reverse osmosis filters, you’ve probably seen a number, followed by the word “GPD”, in the product’s description (such as 50 GPD).

GPD stands for gallons per day, and it’s a way to measure water flow rate in a reverse osmosis water system.

In this guide, we’ve shared everything you need to know about GPD, including what it means, what it measures, what makes a good GPD rating, and more.

πŸ“Œ Key Takeaways:

  • GPD, or gallons per day, is a rating that’s used to estimate the number of gallons of water produced by a reverse osmosis system per day.
  • The average RO water filter system has a GPD rating of 50-100.
  • Factors affecting a water filter’s GPD rating include the filter size, the water pressure, and the number and complexity of the filter stages.

πŸ€” What Does GPD Mean For Water Filters?

GPD, or gallons per day, is a measurement of the flow rate of water in a filter. GPD is usually used as a specification for reverse osmosis systems.

πŸ’‘ Gallons per day is the volume of purified water produced by the system in a single day, measured in gallons.

RO systems have a different flow measurement than other water filters. The flow rate in most standard, non-RO water filters are measured in gallons per minute (GPM), not gallons per day.

Water from a reverse osmosis system measured in gallons per day or GPD

πŸ“ˆ What’s A Good GPD Rating For RO Systems?

Wondering what GPD rating is a sign of a good reverse osmosis system?

For residential use, the minimum required water flow rate for an RO system is 50 gallons per day (GPD).

It’s highly unlikely that you’ll actually use 50 gallons of water in a day. But this rating indicates that the RO membrane can produce filtered drinking water at a suitable enough speed that equates to about 1 gallon of water per hour, if you have a water pressure of about 60 PSI.

The best reverse osmosis water filters have a much better flow rate than 50 GPD. Some RO systems have a flow rate of 75-100 GPD, while a select few have flow rates of 500-800+, producing pure water almost on demand.

πŸ”Ž What Factors Affect A Water Filter’s GPD Rating?

There are a few factors that affect the GPD rating of a water filter:

Filter Size/ Surface Area

First, the size of the filter and its surface area may have an impact on flow rate.

The larger the filter and the bigger the surface area, the more space there is for water to flow through the media.

That’s why whole home reverse osmosis water systems usually have higher GPD ratings than under-sink systems, which are designed for drinking water treatment only.

usws defender whole house reverse osmosis system after installation

Water Pressure

Your existing water pressure will also affect the flow rate of an RO water filtration system in GPD.

If your feed water flow rate is less than 60 PSI, there will be less force to push the water molecules through the RO membrane, reducing the speed of filtration.

If you have a high water pressure, the feed water will be forced quickly through the membrane, increasing the speed of filtered water production.

Number/ Complexity of Filter Stages

The number and complexity of the filter stages will also affect the GPD rating of a reverse osmosis water filter.

Most RO systems include a sediment filter, a carbon filter, an RO membrane, and a post-filter. Some also include additional filter stages, such as UV purifiers and remineralization filters. Additional filter stages may reduce flow rate due to the extra friction in the RO system.

The more complex the filter design, and the more contaminants removed, the slower the water flow rate.

A reverse osmosis membrane has tiny pores, which reduces flow rate (even with the high pressure used to force water through the system). That means RO systems have slower flow rates than non-RO filters.

Aquatru countertop RO system filter stages

πŸ“ Final Thoughts

GPD (gallons per day) is a rating that’s used to indicate the flow rate of an RO system, based on the gallons of filtered drinking water that can be produced per day.

For optimum water filtration results, look for an RO water filtration system with a flow rate of at least 50 GPD.

  • Laura Shallcross
    Senior Editor

    Laura is a passionate residential water treatment journalist who holds an undergraduate degree in Print Journalism and a master’s degree in Creative Writing. Over a span of 5 years she's written on a range of topics including water softening, well water treatment, and purification processes.

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