Filtering Bacteria From Water – Which Filters Can You Trust?

Bacteria in water is one of the leading causes of disease outbreaks across the U.S. While there are many sources of contamination, there are only a few ways to remove the bacteria from water.

Distillation and UltraViolet water treatment systems are the only systems able to kill bacteria and remove them from water. UltraViolet systems that can remove bacteria will carry NSF/ANSI 55 certification. Boiling, iodine and chlorine addition can remove some bacteria, while water filters do not remove any bacteria from water.

Keep reading to find out

  • Why water filters CAN’T remove bacteria
  • Which water purification systems remove bacteria from water – and WHY
  • The types of bacteria in our water supply
  • Where in our water supply bacteria can grow – some of the places may surprise you.

Do water filters remove bacteria?

There are only 2 types of water purification systems that remove bacteria from water – Distillation and UltraViolet systems.

Water Filtration / Purification SystemRemoves Bacteria
Counter-Top Filters
Faucet-Mounted Filters
Filter Pitchers
Ion Exchange
Reverse Osmosis
Under Sink Filters

First, I will explain why other methods can’t remove bacteria (even though sometimes they claim to), and then I’ll explain the 2 types that do, and how they are so successful at removing bacteria when all other methods of water purification fail!

Water Filters and Purifiers that DON’T remove bacteria

Most water filters and purifiers don’t remove bacteria from water, including:

  • Counter-Top Filters
  • Faucet-Mounted Filters
  • Filter Pitchers
  • Ion exchange
  • Reverse Osmosis
  • Ultrafiltration
  • Under Sink Filters


According to the Centers for Disease Control and Prevention (CDC)

“There is no filter certified to remove bacteria from water”.

Centers for Disease Control and Prevention

With the exception of ion exchange and reverse osmosis, the reason why all filters fail to remove bacteria is the same.

Filters typically rely on carbon filters to remove contaminants from water.

Filters that use activated carbon as their means of treatment are great at removing organic contaminants, chlorine, chlorination byproducts, and even some pesticides. However, according to the CDC an activated carbon filter…

“Does not remove nitrates, bacteria, or dissolved minerals”.

Centers for Disease Control and Prevention

Carbon filters work by trapping contaminants, because of their high porosity and high surface area.

It is the small pore spaces that contaminants enter, where they then adhere to (or stick to) the surface of the carbon filter.

The best case scenario is that the bacteria doesn’t stick around – that it will flow straight through the carbon filter, with the water.

The worst case scenario is that the bacteria grows on the carbon filter, in the tiny pore spaces. This includes granular activated carbon filters and block filters too.

Ion exchange

Ion exchange systems include two types:

  1. Anion exchange
  2. Cation exchange

1. Anion exchange

Anion exchange units treat water as it flows through a resin. The resin contains an anion (a negatively charged ion), such as chlorine.

The anion exchanges (or swaps) with the ions already in the water.

Anion exchange is primarily used for:

  • Dealkalization (reducing pH)
  • Deionization

So, anion exchange is great at removing minerals and even fluoride, but it is unable to remove bacteria.

2. Cation exchange

Cation exchange works much the same way as anion exchange, except that the resin contains a positively charged ion, usually calcium or magnesium.

Cation exchange is mainly used for

  • Deionization
  • Demineralization (water softening)

But once again, cation exchange is useless against bacteria.

Reverse Osmosis

Reverse osmosis is one of the best methods of water purification available. Between its pre-sediment filter, carbon filter and semi-permeable membrane you would think that reverse osmosis would easily remove bacteria from water.

But, this is not the case.

Reverse osmosis removes nitrates, sodium, organic compounds, pesticides and even some petrochemicals.

But even the membrane’s very tiny pore size of less than 1 micron isn’t enough to remove bacteria from water.

Water Filters and Purifiers that DO remove bacteria

There are literally only 2 methods of water purification that are able to remove bacteria.

  1. Distillation
  2. UltraViolet

1. Distillation

Distillation treats water by boiling it. As the water evaporates, turning to steam, all of the contaminants in the water are left behind.

The steam is then cooled and captured as liquid water ready to drink.

Unlike other contaminants, bacteria isn’t just left behind when the water evaporates, the bacteria is killed.

Amazon sells a range of distillers. I like this distiller (affiliate link) because it is easy to install and just sits on your counter – ready with water for you and your family to drink.

However, it is important to be careful – a strict cleaning routine of the unit should be maintained, and the unit switched off and cleaned when not in use. Because the CDC says…

“Bacteria may recolonize on the cooling coils during inactive periods”

Centers for Disease Control and Prevention

Which means any water in the storage tank could become infected with bacteria again.

2. UltraViolet

UltraViolet water treatments systems may not be effective at removing chemicals or metals, but they are amazing at removing bacteria.

BUT, just because UltraViolet systems are able to remove bacteria doesn’t mean that ALL systems can. Only systems that carry National Sanitation Foundation (NSF) certification for the removal of bacteria are able to do so!

Under the NSF these systems are called ‘UltraViolet Microbial Water Treatment Systems’ and carry certification NSF/ANSI 55.

These are labeled Class A systems.

According to the NSF, these systems are designed to

“…disinfect and/or remove microorganisms, including bacteria and viruses, from contaminated water”.

NAtional Sanitation Foundation

So, how do these UltraViolet systems actually remove bacteria from water?

Well, there are 3 types of UltraViolet (UV) light:

  • UVA
  • UVB
  • UVC

UltraViolet light is short wavelengths of light that are not visible to the human eye. The shorter the wavelength, the more harmful the UltraViolet radiation.

According to the World Health Organisation…

“Short-wavelength UVC is the most damaging type of UV radiation”.

World health organisation

And you probably guessed it, UltraViolet water treatment systems use UVC light to kill microorganisms, such as bacteria.

The UltraViolet light works by disrupting the very DNA of the bacteria, killing them in their tracks.

One thing to know about UltraViolet water treatment systems is that their ability to kill bacteria depends on the UltraViolet light being able to reach the bacteria in the water.

That means if there is a lot of sediment in the water the light may not penetrate and kill all the bacteria.

A simple solution is to use a pre-sediment filter before the water reaches the UltraViolet system, to remove anything that could reduce its effectiveness. However, this is not normally needed because our drinking water doesn’t usually have a lot of sediment – although, sometimes residents using well water may need one.

If you want to protect yourself and your family from harmful bacteria in water then you can purchase an UltraViolet water treatment system. I recommend this UltraViolet system from Amazon (affiliate link), because it actually has NSF-55 certification.

Other options?

The CDC also says that treatment with iodine, chlorine dioxide or chlorine can be effective at removing some bacteria from drinking water.

Remember, the most important thing to know about bacteria in your drinking water is actually KNOWING whether it is in your water, or not.

Why do I think that is the most important thing? – Because, if you know that you have harmful bacteria in your water then you won’t drink it!

It is particularly important to check for bacteria in your water if you use a domestic well for your drinking water supply – which are whopping 15% of Americans do!

If you use city water for drinking then you may also want to test for bacteria in your tap water if any of the following apply to you:

  • Recently moved home
  • Had plumbing work done recently
  • Unsure of the last filter change of a water filtration system

You can easily test your water at home for bacteria. Kits that test for bacteria in drinking water are cheap and easy to use, so there is no reason not to find out if they are in your water.

I recommend this bacteria test from Amazon (affiliate link), because it isn’t expensive, has great reviews and you just have to pour some water into the jar, shake and then leave it for 48 hours – simple!

Is there bacteria in tap water?

Water contains many bacteria that are not harmful to us. However, harmful bacteria, such as fecal coliform, E.coli, legionella and salmonella, can contaminate our tap water through sewer overflows or wastewater releases.

Even though some of the nastiest bacteria come from feces contaminated water, surprisingly a study in the journal Water ResearchRef2 found that water purifiers can actually introduce bacteria to our drinking water.

In particular, carbon filters can provide a home for bacteria to grow on. Especially if they are not cleaned or replaced regularly.

Unlike filters, distillation and UltraViolet water treatment systems remove all the different types of bacteria. Some of the infamous bacteria that you may have heard of, or should be particularly concerned about are:

  • Fecal coliform
  • Escherichia coli (E.coli)
  • Legionella
  • Salmonella

1. Fecal coliform

Fecal coliform are a group of bacteria that live in the gut and feces of animals.

Usually, if fecal coliform is found in drinking water it means that other germs are also surely present!

It’s these harmful germs that can make us sick, including:

  • Diarrhea
  • Dysentery
  • Hepatitis

Fecal coliform is not typically found in tap water because city water is disinfected by community and public water systems. But anyone living on well water needs to be extra careful.

Testing for bacteria is really the only way you can know if your water is clear of bacteria and safe to drink.

2. Escherichia coli

Escherichia coli is better known as E. coli and is a major species of fecal coliform.

When E. coli is found in our drinking water it is an indicator that the water is contaminated by fecal pollution and is definitely not safe to drink. This is because unlike some other types of fecal coliform E.coli does not occur naturally in the environment, but only in feces.

It can come from the feces of many warm blooded animals, including:

  • Chickens
  • Cows
  • Pigs
  • Sheep

3. Legionella

The Legionella bacteria can cause a nasty infection called Legionnaire’s disease, and usually leads to pneumonia.

The bacteria is found in almost all types of water and can even be found in your drinking water supply after it has been treated.

According to the Environmental Protection Agency (EPA)…

“Legionella bacteria occupy niches in our potable water supply that are suitable for their survival and growth”.

u.s. environmental protection agency

These include:

  • Components of water distribution systems
  • Cooling towers
  • Whirlpools

This is because they provide a place for the bacteria to grow and multiply and then spread.

4. Salmonella

Salmonella causes a nasty infection in our gastrointestinal tract called Salmonellosis that can make us very sick, and even die – although that’s rare.

Salmonella from the feces of humans or animals makes its way into our water supply by:

  • Agricultural runoff
  • Sewage overflows
  • Sewage systems that are not working properly
  • Polluted storm water runoff

Unfortunately, more often than not we get infected by salmonella because people preparing food do not wash their hands properly after using the restroom.

Apparently, Salmonella was the cause of 53% of all foodborne disease outbreaks from 2006 to 2017.

According to a study in the journal Frontiers in Public HealthRef2, salmonella can also survive and be transmitted in irrigation water.

So, we can ingest salmonella bacteria from a range of sources, but the biggest is from our water supply. In particular, untreated water like well water, but outbreaks can also occur in the community water systems too.

Which water filters remove bacteria?

Currently, there are no water filters that effectively remove bacteria.

Only distillation (boiling) or UltraViolet water treatment systems can remove bacteria from water.

Does a Brita filter remove bacteria?

This is a question that actually gets asked a lot. But, just like all other water filters Brita filters are not effective at removing bacteria from water.

Can bacteria grow on water filters?

Bacteria can grow on all types of water filter. Filters act as traps and reservoirs for sludge, scale, rust, algae or slime deposits. These ‘deposits’ or build-ups provide the perfect environment for bacteria to grow.

A study in the journal NatureRef3 found that both Point of Entry and Point of Use water filtration and purification devices can deteriorate the quality of tap water.

In Ann Arbor, tap water was tested before and after treatment by faucet-mounted filters. The study, published in the journal Environmental Science: Water Research & TechnologyRef4, found that the water coming out of the faucet-mounted filter contained up to 100 times MORE bacteria than the water going into the filter.

The fact that bacteria are able to grow on filters is one of the main reasons why filters should be changed according to the manufacturer’s instructions. This can typically be anywhere from 6 months to 1 year.

Chlorine is usually used to disinfect water and can kill some bacteria, however, bacteria found growing on carbon filters have been found to survive a normal dosing of chlorine. This means that you cannot always trust traditional water treatments to kill bacteria.

However, by simply maintaining any type of water filtration or purification system you have – especially by changing your filters regularly, you can at least ensure your system does not become a home for bacteria!

Related Questions

Do water filters remove amoeba? Some water filters can remove amoeba. These filters are usually NSF-53 or NSF-58 certified and/or have an “absolute” pore size of 1 micron or smaller. Reverse osmosis water purification systems are also able to remove amoeba from tap water. This is because the semi-permeable membrane has a very small pore size. You can read more about amoeba in tap water and how to remove them in this post.

Do water filters remove parasites? Reverse osmosis systems and some water filters can remove parasites from water. The semi-permeable membrane of a reverse osmosis system removes the parasites as the water is pushed through the membrane. Only water filters that carry NSF-53 or NSF-58 certification and/or have an “absolute” pore size of 1 micron or smaller will remove parasites. If the water filter only has a ‘nominal’ pore size of 1 micron then as much as 30% of parasites, like Cryptosporidium and Giardia can pass through the filter and remain in your drinking water. Carbon and activated carbon filters, UltraViolet systems, water softeners, and pentiodide resins will NOT remove parasites.


  1. Liu, G., Zhang, Y., van der Mark, E., Magic-Knezev, A., Pinto, A., van den Bogert, B., … & Medema, G. (2018). Assessing the origin of bacteria in tap water and distribution system in an unchlorinated drinking water system by SourceTracker using microbial community fingerprints. Water research138, 86-96.
  2. Liu, H., Whitehouse, C. A., & Li, B. (2018). Presence and persistence of Salmonella in water: the impact on microbial quality of water and food safety. Frontiers in public health6, 159.
  3. Nriagu, J., Xi, C., Siddique, A., Vincent, A., & Shomar, B. (2018). Influence of household water filters on bacteria growth and trace metals in tap water of Doha, QatarScientific reports8(1), 1-16.
  4. Wu, C. C., Ghosh, S., Martin, K. J., Pinto, A. J., Denef, V. J., Olson, T. M., & Love, N. G. (2017). The microbial colonization of activated carbon block point-of-use (PoU) filters with and without chlorinated phenol disinfection by-productsEnvironmental Science: Water Research & Technology3(5), 830-843.

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