Do Water Filters Remove Bacteria?

At least 1.1 million people in the U.S. get sick each year from germs in drinking water (roughly 1 in 300 people!). That doesn’t mean tap water is unsafe by default, but it does mean bacteria in drinking water isn’t a theoretical issue.

So, do water filters remove bacteria? In short, some do – but many standard household filters don’t.

If you’re using a basic jug filter, it’s probably designed to improve taste and reduce chlorine. That’s useful, but it’s not the same as removing living microorganisms. To deal with bacteria, a filter needs specific technology that’s tested for microbiological treatment.

Here’s what that actually means for you…

 

What Bacteria Can Be Found In Tap Water?

Even treated tap water can contain microorganisms. Most are removed or inactivated during treatment, but some can still appear in certain situations – especially if there are plumbing issues, ageing pipes, or local system failures.

The main microbiological contaminants in drinking water are:

• Bacteria

• Viruses

• Protozoa such as Giardia and Cryptosporidium

Here are some of the most common bacteria in tap water: 

 

Legionella

Legionella is the most commonly reported cause of waterborne illness outbreaks in the U.S, according to the CDC. It doesn’t usually come straight from the treatment plant. 

Instead, it tends to grow inside building plumbing systems, particularly in warm, stagnant water such as storage tanks and hot water systems. People are typically exposed by inhaling contaminated water droplets instead of drinking it.

 

E. coli and Other Coliform Bacteria

E. coli and other coliform bacteria are essentially warning signs. Although they may not make you sick themselves, if they show up in a water test, the water may have come into contact with waste somewhere along the line.

Public water systems check for these bacteria routinely. If E. coli is detected, authorities usually act fast and issue a boil water notice while the problem is fixed. It’s not something you see often in treated city supplies, but it can happen (especially after flooding, damaged pipes, or issues at the treatment plant!). 

 

Giardia And Cryptosporidium

First of all, Giardia and Cryptosporidium are not bacteria, they are protozoa. However, they are still relevant when discussing microbes in drinking water.

Giardia and Cryptosporidium can survive in surface water and are resistant to some forms of treatment. Regulations require very high removal or inactivation rates, but outbreaks have happened in the past, particularly where treatment systems failed or were overwhelmed. They’re more commonly associated with untreated water sources such as lakes or private wells. 

 

Other Opportunistic Bacteria

Some bacteria naturally occur in water at low levels and aren’t usually harmful to healthy people. However, they may pose a risk if you have a weakened immune system.

These organisms often grow within plumbing systems, instead of originating from the main water supply. Stagnant water, biofilm inside pipes, and warm temperatures can all create conditions where bacteria can multiply.

This means the water leaving the treatment plant and the water coming out of your tap aren’t always identical.

For most households on regulated municipal water, serious bacterial contamination is uncommon. But it isn’t impossible… which is why some people choose filtration systems specifically designed for microbiological reduction.

 

Can Water Filters Remove Bacteria?

Yes, water filters can remove bacteria – but only certain types of water filter. A standard carbon filter (often marketed as a water filter that removes chlorine) is built to improve taste and reduce chemicals. It does not reliably remove bacteria.

To remove or inactivate bacteria, you need one of the following:

• Ultrafiltration (UF) membranes around 0.2 microns. These physically block most bacteria.

• Reverse osmosis (RO) systems tested for microbial reduction.

• UV disinfection systems, which inactivate bacteria using ultraviolet light.

To determine whether water filters remove bacteria, check the product description. If the product description only talks about chlorine, taste, or odor, it’s not a bacteria filter.

Certification is a useful shortcut. Filters tested to standards such as NSF/ANSI P231 or 244 are evaluated for microbiological purification. UV systems are commonly tested to NSF-55. If you don’t see any references to this kind of testing, it’s reasonable to assume bacteria removal isn’t its purpose.

 

How Do Water Filters Remove Bacteria?

It depends on the filter – different systems solve the problem in different ways:

1. Ultrafiltration works like a physical barrier. The membrane pores are small enough to trap bacteria while allowing water through.
2. Reverse osmosis pushes water through a dense membrane under pressure. That membrane blocks a wide range of contaminants, including many microorganisms.
3. UV systems take a different approach. They don’t filter bacteria out – instead, they disrupt the bacteria’s DNA so they can’t reproduce. The organisms remain in the water but are no longer able to cause infection.

Each method has its own pros and cons. RO systems can waste some water during filtration. UV systems require electricity and bulb replacement. Membranes need regular maintenance.

The right choice for you depends on what you’re trying to solve – if your concern is chlorine taste, a simple carbon filter is fine. If your concern is bacteria, then you need something more specific.

 

Can Bacteria Grow In Water Filters?

Yes, ironically, bacteria can grow in water filters. A chlorine water filter removes the disinfectant that helps suppress microbial growth. However, if water sits inside the cartridge for long periods, especially at room temperature, bacteria can multiply.

This does not mean that filters are dangerous – it means you should keep your water filter clean. This means you should: 

1. Replace cartridges on schedule
2. Avoid leaving water sitting for days
3. Clean the housing if recommended

So, a poorly maintained filter can create the very issue you were trying to avoid.

So, Which Water Filters Are Best For Removing Bacteria?

If your main goal is to remove bacteria, look for clear wording such as:

• “Microbiological purifier”
• “Bacterial reduction”
• Ultrafiltration around 0.2 microns
• Reverse osmosis tested for microbial removal
• UV disinfection certification
  
  

Basic water filters that remove chlorine will not provide the same protection.

If you need help deciding on the best option for you, see below: 

 

For a compact, multi-stage option, our Alchemy Automatic Water Filter Pitcher is designed to go beyond basic chlorine reduction. The Alchemy pitcher removes 99% of contaminants with effortless maintenance – including 99.99% removal of E. coli. Get yours today!