Microfiltration vs Reverse Osmosis: Difference + What to Use

Written by: Alexandra Uta // Last Updated: Jun 16, 2023

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Microfiltration and reverse osmosis – what might seem quite similar at first glance is actually very different.

Each water treatment method comes with its own advantages and disadvantages. It’s important to understand what each of brings to the table if you’re planning to invest your money in either one.

So, what’s the difference between microfiltration and reverse osmosis, and which should you choose?

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Key Takeaways

Both reverse osmosis and microfiltration use filter elements with fine pores to remove contaminants from water. But the pores on an RO membrane are much smaller (0.0001 microns) than in microfiltration (0.1-10 microns). As such, RO is much more effective at removing a wider range of water contaminants.
Microfiltration is only good for removing bacteria and sediments. RO is ideal if you want to target viruses, cysts, organic, and ions such as lead, chromium, or fluoride.
The downside to reverse osmosis is that it is slower, more expensive, and it produces wastewater.

What Is Reverse Osmosis (RO)?

Reverse osmosis involves pushing water through a thin, semipermeable membrane at a very high pressure level. Water molecules make it through the membrane’s pores and reassemble at the other end into pure fresh water. Everything else, which means all contaminants and impurities, get rejected.

Reverse osmosis systems for home use mostly come in the form of countertop and under-the-sink units. They feature several additional filtration stages to boost contaminant reduction.

What Is Microfiltration (MF)?

Microfiltration is similar to reverse osmosis in that it relies on a surface filter with very small pores. However, filtration is achieved by simply limiting the size of what can pass through the membrane. Water isn’t actually broken down into molecules as in reverse osmosis. Also, pore sizes are much, much larger when compared to RO. As a result, far fewer contaminants get blocked by a microfilter.

Besides, microfilters are usually portable water filters to be used outdoors. They allow you to drink from a non-potable water source that may contain waterborne bacteria.

Difference Between Microfiltration and Reverse Osmosis

Now that we’ve seen how microfiltration and reverse osmosis are similar and different on the surface, let’s take a deeper look into how they work and what they can do. There are quite a few differences to be discovered. It’s important to understand those if you’re planning to invest in either of the two systems.

Contaminant Removal – Which System Is Healthier?

Reverse osmosis is much better at removing water contaminants. Pretty much nothing can make it through a reverse osmosis membrane. The only exceptions are some dissolved gases and few pesticides.

Microfiltration on the other hand only removes bacteria and suspended solids – due to the filter pores being rather large:

Microfilters have pores around 0.1 to 10 microns in size. That seems pretty small, but it doesn’t capture most water contaminants like viruses, organic, salts, heavy metals, etc.
The pores on a reverse osmosis membrane, on the other hand, are as small as 0.0001 microns. This can effectively capture all microorganisms, all organic compounds, and the vast majority of dissolved ions.

Method	Pore Size	Impurities Removed
Microfiltration	0.1-10 Microns	Sediments and Other Suspended Solids, Bacteria
Ultrafiltration	0.01-0.1 Microns	Sediments and Other Suspended Solids, Bacteria, Larger Viruses
Nanofiltration	0.001-0.01 Microns	Sediments and Other Suspended Solids, Bacteria, Viruses, Organic Compounds
Reverse Osmosis	0.0001 Microns	Sediments and Other Suspended Solids, Microorganisms, Organic Compounds, Dissolved Ions

Pre-Filters

Since reverse osmosis membranes are negatively affected by the presence of various contaminants in the input water, pre-filtration is important. Most reverse osmosis systems incorporate a set of sediment and carbon pre-filters that remove sand, silt, dust, and other dirt in order to prevent membrane clogging. Activated carbon also removes chlorine which could damage an RO membrane irreversibly.

Mineral Content

One minor downside to reverse osmosis being so effective is that it removes practically everything from water. Unfortunately, this includes some healthy minerals that are normally good for your diet.

Wastewater

Another problem with reverse osmosis is that it wastes a lot of water as part of its operation. The ratio is pretty bad by default – around 3-5 gallons of wastewater per gallon of purified water. However, steps can be taken to mitigate that and make the process more economical. For example, electric pressure pumps can reduce wastewater by more than 90 percent.

Keep in mind that no matter what you do, some water will still get wasted in the end. That’s just a natural part of the operation of reverse osmosis systems and there is nothing you can do about it. That’s not to say that this water is completely useless, though. You can still use it for various household purposes which don’t require pure fresh water. Just make sure that you never mix it with your drinking water, of course.

Filtration Speed and Water Storage

Another common issue with reverse osmosis is that it works very slowly. It’s not very practical to wait for the reverse osmosis filter to do its job every time you want to drink some water. Because of this, most people invest in storage tanks and attach them to their reverse osmosis systems. In fact, most reverse osmosis systems come with an integrated storage tank in the first place. That’s a standard part of reverse osmosis setups these days.

This isn’t a problem with microfiltration. The process works fast enough that you can drink water as it’s being filtered, usually. But if you’re using a filter with particularly tiny pores, that might not be the case.

Installation Requirements

As mentioned, microfilters are usually portable and don’t require installation. And those microfiltration systems intended for home use are pretty simple to install, all things considered. Their maintenance requirements tend to be relatively low as well.

On the other hand, reverse osmosis systems are more complex to set up and might require professional work in their installation.

Cost

Reverse osmosis systems are somewhat expensive compared to many other types of water filters. $200 is the absolute minimum. Meanwhile, you can buy a microfiltration system for less than $50 in some cases. Reverse osmosis systems also end up more expensive in their maintenance in the long run. This is not a problem with microfiltration systems, where the replaceable parts are usually as cheap as the main system itself.

Applications

Reverse osmosis is used for home water purification as well as in industrial applications:

Seawater desalination
Wastewater treatment
Municipal water purification
Dairy industry
Maple syrup concentration
Dye concentration

Microfiltration can also be found in these places often used for pre-treatment.

What Are the Pros and Cons of Using Microfiltration vs Reverse Osmosis

Reverse Osmosis Pros

Thorough filtration – one of the best methods for purifying water available on the market
Greatly improves how your water tastes and smells
Provides healthy drinking water
Low maintenance requirements – you don’t have to put a lot of work into keeping the system running in the long term
Stop buying bottled water – enjoy fresh filtered water on demand at home

Reverse Osmosis Cons

Wastes a lot of water – this can be improved, but the process is still far from perfect in this regard
Works slowly – you need to use a storage tank to have immediate access to filtered water
Removes healthy minerals – you can compensate for that with the use of supplements
Requires pre-filtration for optimal operation

Microfiltration Pros

Relatively inexpensive – most filters are cheap and widely available
Doesn’t use any chemicals – environmentally friendly
Fast
No wastewater
Retains healthy minerals

Microfiltration Cons

Doesn’t remove all contaminants – additional filtration might be required

Further Reading:

Microfiltration vs. Reverse Osmosis – So Which Is Better?

So, microfiltration vs reverse osmosis – which of the two is better? Which should you use?

Well, neither of the two filtration methods is inherently better. Both have their advantages and disadvantages as you can see above. The important thing to understand is that both methods have been designed for a different purpose:

If you’re dealing with tricky contaminants that normal microfiltration doesn’t remove, you need to go with reverse osmosis. It’s much more effective than microfiltration which will only remove bacteria and sediments. Reverse osmosis removes everything else, too.

But it’s slower and it can’t be used when you are out and about. You need a plumbing system with water pressure or a power connection for a booster pump. So if you are looking for a portable water filter to be used outdoors, reverse osmosis is not it.

Besides, it’s a good idea to start your research by analyzing your water supply and having it tested for contaminants. This doesn’t cost a lot of money, and you typically only have to wait a couple of weeks to receive your results. Once you have them, you will know exactly what kinds of contaminants you’re dealing with, and this will allow you to pick a filtration system that works best for your current needs.

What About Ultrafiltration and Nanofiltration?

The main difference between microfiltration, ultrafiltration, and nanofiltration is the pore size.

Microfiltration pores are usually between 0.1 and 10 microns.
With ultrafiltration, the size can go down to below 0.01 microns.
And with nanofiltration, you have pores as small as 0.001 microns.

Smaller pores can capture more contaminants. However, they also introduce some disadvantages, such as restricting the flow rate of water.

Typically, ultrafiltration and nanofiltration are only used when there is a strict need for them. If you’re not dealing with contaminants small enough to necessitate the use of particularly small filters, it’s probably a waste of money to invest in a solution like that.

If you have any questions about microfiltration and reverse osmosis please don’t hesitate to leave a comment below!

About the Author Alexandra Uta

Alex is a content writer with an affinity for research and a methodical attention to detail. Since 2020, she has fully immersed herself into the home water treatment industry only to become an expert herself. Alex has been using water filters and similar products for years which has gained her lots of hands-on experience.
Learn more about Alex and the rest of the BOS Team.

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