Water filters certified to NSF/ANSI 244 or P231 standards can effectively remove bacteria. Distillation and UltraViolet water treatment systems (certified to NSF-55 standards) are able to kill bacteria in water. Boiling, iodine and chlorine addition can remove some (but not all) bacteria.
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.
Water Filters That Remove Bacteria
Drinking water treatment technologies that are recommended by the CDC to have a VERY HIGH effectiveness at removing bacteria include:
| Water Treatment Technology | Pore Size | Removes Bacteria |
|---|---|---|
| Ultrafiltration | ~0.01 micron | ✔ |
| Nanofiltration | ~0.001 micron | ✔ |
| Reverse Osmosis | ~0.0001 micron | ✔ |
| Distillation | N/A | ✔ |
| Ultraviolet (UV) systems (that include pre-filtration) | N/A | ✔ |
| Counter-Top Filters | ✘ | |
| Faucet-Mounted Filters | ✘ | |
| Filter Pitchers (certified to NSF-244 or -P231 standards) | ✔ | |
| Ion Exchange | ✘ | |
| Under Sink Filters | ✘ |
Drinking water treatment technologies that should be avoided include:
- Microfiltration (pore size ~0.1-microns) – MODERATE effectiveness at removing bacteria
- Water softeners (ion exchange) – NOT effective at removing bacteria
Water Filters and Purifiers that DO NOT remove bacteria
Most water filters and purifiers don’t remove bacteria from water, including:
- Counter-Top Filters
- Faucet-Mounted Filters
- Filter Pitchers (except a rare few)
- Ion exchange
- Under Sink Filters
Filters
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.
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 don’t stick around – that it will flow straight through the carbon filter, with the water.
The worst case scenario is that the bacteria grow on the carbon filter and in the tiny pore spaces. This includes granular activated carbon filters and block filters too.
Ion exchange
Ion exchange systems include two types:
- Anion exchange
- 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.
Water Filters and Purifiers that DO remove bacteria
There are very few methods of water purification that are able to remove bacteria.
- Distillation
- Reverse Osmosis
- UltraViolet
- Silver (a new method!)
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 aren’t just left behind when the water evaporates, the bacteria is killed.
However, it’s important to regularly clean your distiller as bacteria can quickly recolonize on the cooling coils when you’re not using it. If this does happen, you may get bacteria growing in the storage tank – the water that you use – which kind of defeats the purpose of using a distiller in the first place.
So, just make sure you empty out all of the water and let it air dry when not in use. It also wouldn’t hurt to wipe it down with a vinegar and water solution once in a while to kill off any surface bacteria and remove any biofilm.
Amazon sells a range of distillers that will all be effective at removing bacteria. This Megahome distiller from Amazon is well priced and has a glass storage tank, which is hard for bacteria to grow on and is easier to clean:
2. 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.
Reverse osmosis removes nitrates, sodium, organic compounds, pesticides and even some petrochemicals.
But it is the membrane’s very tiny pore size of 0.0001 micron that is small enough to remove bacteria from water.
Water Purification Guide has more detailed information on specific reverse osmosis systems able to remove bacteria available here.
3. 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. UV systems that carry National Sanitation Foundation (NSF) certification for the removal of bacteria can be trusted.
Systems should be tested to NSF/ANSI 55 standards and are called ‘UltraViolet Microbial Water Treatment Systems’. Although NSF certification is voluntary, reputable UV products will do so to prove they actually remove bacteria (and other microorganisms including viruses).
Ultraviolet Microbial Water Treatment Systems will be labeled Class A or Class B systems.
- Class A systems can inactivate pathogenic organisms using a UV dose at the energy wavelength of 254 nm (40 mJ/cm²).
- Class B systems can inactivate non-pathogenic organisms using a lower UV dose at 16 mJ/
These are labeled Class A systems.
Types of UV:
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 Worle Health Organization, short-wavelength UVC is the most damaging type of UV radiation.
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.
It’s important that a pre-sediment filter is used before the water reaches the UltraViolet system. If there is sediment in the water the light may not completely penetrate and kill all the bacteria.
UV systems are typically added to Whole House Systems or Reverse Osmosis Systems after as the final filtration / sterilization stage to make sure the water is completely free of microorganisms.
UV For Whole House Systems
Most people buy a UV water treatment system larger than what is needed to keep up with high demand periods. The example below, from HQUA, is a UV whole house sterilizer (12 GPM) that comes with 1 extra UV lamp and 1 extra quartz sleeve.
UV For Reverse Osmosis Systems
Most Reverse Osmosis systems deliver purified water to accommodate the flow rate to one or maybe three water outlets (e.g. the faucet, dishwasher, or refrigerator). It’s a bit cheaper for this kind of set up compared to a whole house system and the UltraViolet sterilizer can be a lot smaller as the flow rate off an RO is typically lower.
This RO comes with everything you need, including the UV Sterilizer for killing bacteria. The best thing about this Express Water RO system is the UV component has a warning light that alert you when the power of the UV falls below the germicidal range to keep you and your family safe.
4. Silver
Several brands of water filter pitcher now combine silver technology with incredibly small pore sizes in their filters. This makes them able to remove bacteria and inhibit their growth.
Very few water filter pitchers are capable of removing bacteria, but here are some that do.
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.
Types of 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.
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 different 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 are 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”.
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.
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.
Water Filters that Remove Bacteria
For tap water that has been treated to public water system standards, you can trust water filters to remove bacteria if they have been tested to NSF/ANSI standards 244 or P231. These systems will also be able to remove cysts and viruses.
Believe it or not, there are very few water filters that carry these certifications.
Two that we highly recommend are Clearly Filtered (NSF-244 certified) and the Epic Water Nano (NSF-P231 certified):
Clearly Filtered Water Filter Pitcher
| Bacteria | % Removed |
|---|---|
| E. Coli | 99.99 |
| Klebslella spp. | 99.99 |
Clearly Filtered pitchers are also capable of removing 99.99% Giardia, Cryptosporidium, Algae, Amoeba, Cysts and 99.9999% of viruses (including MS2 Phage and Rotavirus).
Epic Water | Nano Water Filter Pitcher
| Bacteria | % Removed |
|---|---|
| Pseudomonas aeruginosa | 99.9999 |
| E. Coli | 99.9999 |
| Klebslella pneumoniae | 99.9999 |
The Epic Nano can also remove 99.999% Giardia (protazoan flagellates), Cryptosporidium (parasites), and 99.95% of MS2 Phage (virus).
Do Brita Filters Remove Bacteria?
This is a question that actually gets asked a lot!
Brita filters are certified to NSF standards 42, 53, and some Brita products are also certified to NSF standard 401. However, these certifications have nothing to do with the removal or reduction of microbiological contaminants including bacteria, viruses, or parasites.
Brita filters are not designed to purify water and should not be used with water that is microbiologically unsafe or if the water quality is unknown (e.g. during a boil water advisory or from a private well).
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!
Do water filters remove amoeba?
Amoeba are not bacteria but single-celled protozoa.
Some water filters can remove amoeba.
These filters are usually NSF-244 or -P231 certified and/or have an “absolute” pore size of 1 micron or smaller. Clearly Filtered water pitchers specifically state they remove amoeba.
Reverse osmosis water purification systems are also able to remove amoeba from tap water, because of the very small pore size of the membrane (typically 0.0001 micron) and should be certified to NSF-58 standards.
Water Purification Guide has more detailed information about amoeba 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 parasites as water is pushed through the membrane.
Only water filters that carry NSF-244, P231 or NSF-58 (for reverse osmosis only) 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.
References
- 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 research, 138, 86-96.
- 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 health, 6, 159.
- 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, Qatar. Scientific reports, 8(1), 1-16.
- 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-products. Environmental Science: Water Research & Technology, 3(5), 830-843.
