Do RO Systems remove bacteria? The Simple Answer

RO System Water Purifier

Do RO systems remove bacteria? Flickr Commons image via Wuestenigal

Do reverse osmosis water purifiers actually remove bacteria from your water?

In order to answer this question, it's important to understand the stages of filtration in an RO system. In fact, the term "reverse osmosis" actually refers to a particular stage within a water purification system.

Read more: Best water purifiers and filters

The Reverse Osmosis membrane is the part of a water purifier that can remove extremely small elements, which includes certain kinds of viruses and bacteria.

However, for making certain you're removing as much bacteria as possible, I'd recommend a second filtration stage - ultra-violet (UV) light.

Read more: Reverse osmosis filtration

Ultra-Violet Light and RO Membrane

In order for an RO system to remove bacteria from your water, I'd recommend making sure that your RO system has the following stages:

  • RO membrane
  • Ultra-violet light

If it does, the unit should be fairly effective when it comes to removing bacteria from your water. Even with just the reverse osmosis membrane, bacteria is going to have a hard time getting through.

What bacteria does a reverse osmosis membrane remove?

But what bacteria will be removed?

Per the CDC, the following are the most common:

  • Campylobacter
  • Salmonella
  • Shigella
  • E. coli

Viruses are also easily removed by RO systems, namely the following:

  • Enteric
  • Hepatitis A
  • Norovirus
  • Rotavirus

Often times the UV light filter will get bacteria or viruses that the RO membrane might leave behind. However, having one or both of these methods is going to be extremely effective at removing the most common contaminants.

Can some bacteria slip through?

While it's also possible for bacteria to make it through these mechanisms, it's unlikely to be enough to then also get past your immune system. Even when you drink unfiltered water, your immune system is extremely good at fighting off common bacteria and viruses. 

Assuming the RO system eliminates 95 percent of the bacteria in your drinking water, the odds of getting sick from that water is dramatically reduced.

What happens to bacteria that RO systems filter out?

Bacteria that is caught in the RO filter will die and eventually be removed when you change the filter. This is partly why it's important to change your RO membrane filter at regular intervals, to avoid the build up of contaminants and bacteria over time.

Even while the bacteria stays in the filter, it does not pose a risk to any additional water that gets passed through.

As long as you remember to change the filter at the recommended intervals, you've got nothing to worry about.

Does a reverse osmosis filter kill the bacteria?

Technically, no.

The RO filter doesn't kill the bacteria, at least not right away. What it does is simply remove it from the water before passing the water through to your faucet. From there, the bacteria will eventually die because it has no host and nowhere to go.

Thus, the RO system is only indirectly responsible for killing the bacteria by removing it from the water.

What about the UV light?

The UV light filter, on the other hand, should actually kill bacteria that the RO membrane might have missed. In most systems that have a UV light filter, it's placed after the RO membrane, sort of as the last line of defense.


In summary, the RO membrane and UV filter - when they team up - are an extremely effective deterrent of bacteria and/or viruses in your drinking water. Combined with your own immune system, they make it highly unlikely that you'll experience any kind of sickness from your source of drinking water.

If you have questions about RO systems or about preventing bacteria from contaminating your drinking water, feel free to drop them in the comments section below and we'll take a look.

1 thought on “Do RO Systems remove bacteria? The Simple Answer

  • It was very reassuring to know that the bacteria coming from the water systems isn’t enough to get a household sick. My wife and I are planning on having our own home water purification system, because we find it very convenient to drink tap water. That being said, we’ll make sure to look for the best ones in town.

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