Microfiltration vs. Ultrafiltration vs. Nanofiltration vs. Reverse Osmosis

Find out the differences between microfiltration, ultrafiltration, nanofiltration, and reverse osmosis to determine which option is best for your home.

By: Maggie Pace

In 2015, the National Resources Defense Council identified more than 80,000 violations of the Safe Water Drinking Act in the U.S. These included failures to meet health standards plus monitoring and reporting shortfalls.

The unfortunate reality is that water quality in homes around the country is inconsistent. And while most U.S. homes have tap water that meets EPA safety guidelines, that doesn't mean your water is germ-free.

This is why the CDC recommends filtration as an extra step to ensure cleaner, safer water in your home. Acting on that recommendation can be challenging, though. Start researching filters and you'll see why. There are different methods of filtration, such as microfiltration, ultrafiltration, nanofiltration, and reverse osmosis. It can feel like you need a science degree to understand which is best.

This guide should clear up the confusion. Let's look at how filtration works generally, the differences between filtration methods, and which option is best for your home.

How does filtration work?

Despite their complicated names, ultrafiltration, nanofiltration, and reverse osmosis are straightforward concepts. All three methods clean water by pushing it through a membrane with tiny holes, which are called pores. Pores are measured in micrometers, abbreviated as um. (One micrometer is one-millionth of a meter.) As water passes through the pores, substances in the water get stuck in the membrane.

Pore size is the primary difference among microfiltration, ultrafiltration, nanofiltration, and reverse osmosis. As you might guess, smaller pores filter out more impurities from the water.

What is microfiltration?

Ultrafiltration membranes are smaller than microfiltration, with pores ranging from 0.01um-0.1um. While smaller than microfiltration, these pores are still larger than what's used in nanofiltration and reverse osmosis. Ultrafiltration will remove bacteria, protozoa, suspended solids, and some viruses. Other viruses can remain, along with dissolved mineral salts and sugars.

Ultrafiltration isn’t recommended for drinking water, but has other applications including:

  • Removing bacteria from milk
  • Producing cheese
  • Processing wastewater
  • Blood treatments, like dialysis
  • Concentrating fruit juice

What is nanofiltration?

The pore size of a nanofilter is 0.001um-0.01um. Nanofiltration will remove the same impurities as ultrafiltration, plus more viruses, organic matter, and salts (like calcium) that create hard water. Other minerals, including sodium chloride, can pass through a nanofilter and remain in the water.

Nanofiltration, like ultrafiltration, has specialty applications including:

  • Softening hard water
  • Removing metals from wastewater
  • Scrubbing pesticides from groundwater

What is reverse osmosis?

Reverse osmosis has the smallest pore size of the three methods, at 0.0001um. Reverse osmosis will remove all organic compounds, all viruses, and most minerals, including calcium, magnesium, salt, and lead. What remains is nearly pure, clear water.

"Reverse osmosis will remove all organic compounds, all viruses, and most minerals, including calcium, magnesium, salt, and lead. What remains is nearly pure, clear water."

Reverse osmosis is a preferred method for purifying drinking water. According to the Safe Drinking Water Foundation, reverse osmosis systems played key roles in ending two multi-year boil orders in Canadian communities. The process is also commonly used in the bottling of spring water. Other applications include water desalination, equipment cleaning, and food and beverage processing.

Difference Between Microfiltration, Ultrafiltration, Nanofiltration, and Reverse Osmosis

The practical difference between ultrafiltration, nanofiltration, and reverse osmosis is the amount of material that's removed from the water. Imagine pouring water through a colander vs. cheese cloth. The colander will filter out large substances, while the cheese cloth will filter out the big stuff plus some smaller materials, too.

If ultrafiltration and nanofiltration are the colander, then reverse osmosis is more like cheesecloth. The tiny pores in a reverse osmosis membrane effectively filter out nearly all particles.

A more scientific explanation of the differences across these methods is shown in the table below.

Which of these options is best?

For water you use in your home, reverse osmosis is the best filtration method. Reverse osmosis filters out up to 99% of contaminants. Microfiltration, ultrafiltration, and nanofiltration cannot reach the same level of purity.

Reverse osmosis has a drawback, though. The process filters out some good minerals along with the bad stuff. Specifically, reverse osmosis strips out calcium, magnesium, and potassium from water. Those three minerals have known health benefits and contribute to the taste of drinking water.

You can combat this drawback by investing in a filter that remineralizes the water. Aquasana's under-sink OptimH2O® Reverse Osmosis + Claryum® does this as part of its four-step purification process:

  1. Water is processed through a carbon filter to remove pesticides and other organic chemicals.
  2. Water is pushed through a reverse osmosis membrane to filter out fluoride, nitrates, nitrites, lead, radium, and arsenic.
  3. The system's Claryum® filter removes heavy metals.
  4. A remineralizer adds back calcium, magnesium, and potassium for taste and health benefits.

OptimH2O® Reverse Osmosis + Claryum®

Combines Claryum® and reverse osmosis technology to remove 88 contaminants including fluoride and arsenic.

Thanks to the multistep filtering, the OptimH2O® Reverse Osmosis + Claryum removes up to 99% of 88 known contaminants. The system is tested and certified to NSF/ANSI Standards 42, 53, 58, and 401 for the claims specified on the Performance Data Sheet in the Owner's Manual.

In summary, reverse osmosis is the highest standard of purification for drinking water. Combine reverse osmosis with remineralization and you'll have pure water that tastes great and is healthful, too.