Reverse Osmosis Pore Size (Complete Guide)

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Reverse osmosis systems use a semi-permeable membrane that has tiny pores, which allow only water molecules and other tiny contaminants to pass through.

Here, we’ve shared everything you need to know about reverse osmosis pore size.

📌 Key Takeaways:

  • Reverse osmosis (RO) systems have a membrane pore size that’s measured in microns and dictates the micron size of the contaminants that are rejected.
  • The average pore size of the membrane in an RO system is 0.001-0.0001 microns.
  • Some of the contaminants removed by reverse osmosis filters include chlorine, lead, heavy metals, bacteria, and fluoride.

🤔 What Is Reverse Osmosis Pore Size?

Reverse osmosis pore size is the size of the pores in a reverse osmosis membrane.

RO pore size is measured in microns. The smaller the measured pore size, the smaller the holes in the semi-permeable membrane, and the smaller the particles that are rejected by the membrane.

You should find information on the pore size of an RO membrane in the product description.

Different ro water filter micron ratings

🔎 Average RO Membrane Pore Size

The average pore size of reverse osmosis membranes is 0.001-0.0001 microns.

The size of the pores depends on the design of the membrane and the materials used.

RO membranes with the smallest pore size have a contaminant rejection rate of up to 99% when filtering a typical household water supply. That makes reverse osmosis filtration one of the most effective water purification solutions for drinking water.

🆚 RO Membrane Vs Water Filter Pore Size

RO membranes have much smaller pore sizes than the average carbon-based water filter. That’s why so many people prefer membrane filtration over particle filtration because of its additional contaminant removal capabilities.

The average pore size of an activated carbon filter is 0.5 microns to 50 microns, depending on the materials used and the filter type and quality.

That’s at least 500x bigger than a reverse osmosis membrane’s pores.

Carbon filter pores are only capable of trapping larger particles, while the semipermeable membrane in a reverse osmosis filter can trap even the tiny, difficult-to-remove particles, like microorganisms.

Filtration spectrum

🆚 RO Membrane Vs UF Membrane Pore Size

Ultrafiltration and reverse osmosis treatment systems often get confused, but these two technologies have slightly different pore sizes and different contaminant rejection rates.

A reverse osmosis system, as we know, has pores that range from 0.001-0.0001 microns.

Ultrafiltration (UF) systems have a pore range of 0.02 – 0.05 microns. This is smaller than a carbon filter’s pores, making UF more capable than standard filtration, but it’s not as small as RO membrane pores.

Unlike RO water filters, ultrafiltration membranes don’t remove all dissolved substances from water. Salts, fluoride, and other dissolved solids and organic molecules are retained in the purified water.

Membrane Filtration Process

📖 How RO Membranes Work

A reverse osmosis membrane works by rejecting all total dissolved solids, including salts, minerals, some microorganisms, chemicals, metals, and other dissolved solids from a water supply.

Water is sent through the reverse osmosis unit under a high pressure, which counteracts the osmotic pressure that’s present during filtration. It’s forced though the membrane, where the pure water molecules are separated from the dissolved solids.

The solids rebound back into the RO chamber, and are ejected from the system in a small amount of wastewater.

Reverse osmosis membrane

⚗️ What Does Reverse Osmosis Remove?

The exact contaminants removed by RO depends on the membrane pore size, as well as other factors including the water quality, flow rate, and membrane age and quality.

Some of the impurities that are generally removed by the RO process are:

  • Organic chemicals
  • Large salt molecules
  • Mineral ions
  • Fluoride
  • Bacteria
  • Some viruses
  • Heavy metals like lead, iron, manganese, and nickel
  • Nitrate
  • Sediments
  • Some VOCs

RO is more effective than any other at-home filtration methods at producing the purest potable drinking water.

The only contaminants that can’t be effectively removed by reverse osmosis are dissolved gases, some chlorine by-products and VOCs, and some tiny viruses.

RKIN U1 countertop RO dispensing cool water

📑 Final Word: Is Reverse Osmosis Better Than Other Filtration Methods?

Reverse osmosis is easily distinguishable from other forms of water treatment due to its tiny pore size.

The main benefit of RO compared to other filters is its ability to remove the majority of dissolved solids.

👨‍🔧 If you want a water purification solution that can treat drinking water effectively, making it as pure and as clean as possible, reverse osmosis is the best option to consider.

However, the small RO membrane pore size has its disadvantages.

The biggest disadvantage of using an RO system with small pores is that contaminants like iron, hardness minerals, and chlorine might clog or foul the membrane wall.

This will reduce the membrane’s efficiency and shorten its lifespan. Reverse osmosis works only when the membrane allows water particles to easily pass through, so you might need to install pre-treatment technologies to prevent clogging of the membrane’s pores.

  • Jennifer Byrd
    Water Treatment Specialist

    For 20+ years, Jennifer has championed clean water. From navigating operations to leading sales, she's tackled diverse industry challenges. Now, at Redbird Water, she crafts personalized solutions for homes, businesses, and factories. A past Chamber President and industry advocate, Jennifer leverages her expertise in cutting-edge filtration and custom design to transform water concerns into crystal-clear solutions.

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