activated carbon or granular in clear bottle

How Do Charcoal Water Filters Work?

Charcoal filters have become very popular in the past few years.  Strong believers in the filters highlight their effectiveness at purifying water plus the fact that they help reduce single-use plastic consumption. Regardless of how clean you think your tap water is, you can also go the extra step to ensure that your water is safe by purchasing an at-home water filter.  Charcoal filters are a great at-home or portable option for a filter that gets the job done.

Black charcoal texture background

Charcoal has been used since the earliest times for many purposes including art, medicine, and most importantly, as fuel.

What is Charcoal?

Charcoal is made by burning wood at extremely high heat and with minimal oxygen.  This process, known as pyrolysis, removes all water and other absorbable substances out of the wood.  The wood will typically be burned inside of a small, tight space in order to suffocate the wood from as much oxygen as possible. Once it is created, charcoal is utilized in an abundance of ways including:

  • Cooking and heating
  • Industrial and automotive fuel
  • Purification and filtration

Many people make charcoal when making a campfire or grilling without even realizing it.  Maybe you’ve been around a fire and noticed how, after burning wood for a long period of time, the visible flame goes away and the wood starts to light up the colors of those flames. 

That is a sign that the wood’s Volatile Organic Compounds (VOCS) have been combusted and that charcoal has been created from the wood. From there, the charcoal can go towards many uses including water filtration.  But, first, if it’s going to be used as a filtration system, then must go through an activation process.

Activated Charcoal

In order for the charcoal to be an effective water purifier, it first needs to be activated. Activated charcoal (also known as activated carbon) is charcoal that has gone through a process in which it is treated with oxygen in order to open up millions of tiny pores on its surface.  The tiny pores are concentrated all over the charcoal’s surface.  

In order to activate the charcoal, it first must be heated up to a temperature as high as 1,650 degrees Fahrenheit!  In addition to oxygen, steam is then added to the presence of the heating charcoal in order to help open up its pores. Once activated, the pores are the basis for the charcoal’s water purification abilities.  The specific process that these little pores create filtered water with is called carbon filtering.

How Charcoal Filters Work: Carbon Filtering

Activated charcoal water filters utilize the technique of carbon filtering to filter out water impurities.  In carbon filtering, activated charcoal adsorbs impurities into its many pores.  The pores then hang tight to the impurities so they don’t make it into your drinking water.  

The key here is the charcoal’s adsorption abilities.  Adsorption (not absorption), physically binds certain chemicals to an object’s surface.  Activated charcoal is a fantastic adsorbent and this chemical attraction traps the impurities in the water to the charcoal’s surface.  Unlike absorption, it does not pull substances within itself such as how a sponge works.  

The effectiveness of a carbon filter depends on two factors:

  1. Activation of the charcoal
  2. Surface area of the carbon

In order to get the most out of your charcoal filter, you’ll want to be sure that your charcoal has been activated with oxygen to the point that the maximum number of pores are open and that the charcoal has a large surface area.  Larger surface areas are achieved by opening up as many small pores as possible.  Smaller pores contribute more to large surface areas than large pores do.  Maximizing the number of small, open pores ensures the highest water quality.

charcoal water filter

What Contaminants Do Charcoal Filters Get Rid of? 

Activated charcoal filters are effective at purifying your water of many common contaminants.  Some of these include:

  • Chlorides
  • Sediments (soil, dirt, etc.)
  • Volatile organic compounds
  • Some heavy metals

To begin with, charcoal water filters effectively purify water of chlorides including chlorine.  Not only does chlorine make water taste bad, but, when ingested in high amounts, it can cause vomiting and even coma.  This explains why some people avoid swimming in swimming pools high in chlorine altogether.  Thankfully, charcoal filters are able to filter out chlorine.   

Next, charcoal filters effectively filter out sediments in the water.  Due to erosion, sediments make their way to the surface of freshwater sources and then slip into our water supply.  Common sediments include dirt, tiny rocks, and sand.  These particles are not particularly harmful, but they are also not particularly pleasant to consume.  Sand, dirt, rocks aren’t usually considered palatable.

Third, charcoal water filters purify water of Volatile Organic Compounds (VOCS).  VOCS is a broad category of contaminants and includes hydrogen sulfide, a foul-smelling chemical compound most commonly found in well water.  Hydrogen sulfide is often attributed to having a smell similar to rotten eggs.  Many other VOCS have foul smells; therefore, charcoal water filters overall improve the smell of drinking water.  

Finally, heavy metals such as lead and arsenic are particularly dangerous for human health.  Many can recall the recent water crisis in Flint, Michigan and that lead poisoning was just one of the issues with the water there.  Lead is extremely toxic and, according to the EPA, can lead to everything from nervous system damage to learning disabilities

Charcoal water filters are able to get rid of some but not all heavy metals including lead.  To avoid heavy metal poisoning, ensure that both your home and your city’s pipes are regularly cleaned and replaced. Unfortunately, activated charcoal filters don’t filter out all water contaminants.  Some that they don’t filter out include:

  • Minerals
  • Fluoride
  • Nitrates and nitrites
  • Microorganisms
  • Dissolved inorganic compounds

First off, charcoal filters don’t catch minerals in your water including calcium, magnesium, and sodium.  For some people, this is good news; minerals in water are naturally occurring and provide a hefty dose of healthy dietary minerals.  For others, however, a high mineral concentration can make water taste bitter.  Depending on whether you enjoy the taste or not, minerals slipping through the filter can be considered a positive.

Secondly, charcoal filters don’t catch fluoride as well as nitrates and nitrites.  Fluoride is naturally occurring in water and is often added to a water supply during the purification process.  This has drawn criticism as fluoride has been shown to cause negative adverse effects including brain and nerve cell damage

Also, nitrate and nitrite chemicals, most commonly found in well water, are dangerous when ingested at high levels.  According to the CDC, they have been shown to cause methemoglobinemia, a disease that reduces oxygen in the blood.  Considering that charcoal water filters don’t rid water of these chemicals, this is a big downside.

Next, charcoal filters don’t catch microorganisms in water.  Some of the microorganisms are pathogens that cause diseases in humans.  They are typically either bacteria, virus, or protozoa and each of them is capable of causing infections including E. coli and various rotaviruses.  

Lastly, charcoal filters won’t catch certain inorganic compounds.  Inorganic compounds are a broad category and include everything from minerals to carbonates and cyanates.  While not all inorganic compounds cause harm to human health, not everyone wants them to be floating around in their water.

In conclusion, charcoal water filters are very effective at purifying water in certain categories but not others.  If you use a charcoal filter, be sure that you or your city or well has the proper filtration systems in place to remove the contaminants that charcoal does not pick up.  For example, reverse osmosis and micron filtration are two effective filtration methods that can help pick up what charcoal filters can’t. 

If you rely on water from your city, check with them to see what kind of filtration systems they have in place.  If you rely on your own well for water, double-check the kind of systems both your well and home have in place. Moreover, if you’re going to use a charcoal filter, use it as a second filtration method on top of another thorough filtration system that rids water of all the things that the charcoal misses.

Water purification filter with activated charcoal and other filter substrates

Charcoal filters are used not just in water purification but also in vacuum cleaners, ovens, air purifiers, compost pails, and even trash cans.

How Effective are Charcoal Filters?

Charcoal filters are an effective water treatment for at-home water purification.  As long as your tap water is being treated to get rid of contaminants either by your city’s water system or your home’s well, then using a charcoal filter is a great way to clean out the remainder of contaminants that slip through after treatment. There are a couple of ways you can ensure your charcoal filter is most effective including:

  • Maintaining water flow
  • Regular filter replacement
  • Optimal pore size

To begin with, charcoal filters are more effective when they are in contact with water for longer periods of time.  Therefore, water that flows through the filter very quickly will be in contact for less time and the water won’t be as well treated.  So, try to slow down the speed at which water goes through the filter in order to make the most of it.

Additionally, regularly replacing your filter is critical to ensuring it works properly.  Over time, the charcoal’s pores become saturated with contaminants and can no longer adsorb any more contents.  Therefore, aim to switch out your charcoal filter at least once every 12 months.

Lastly, the size of the pores on the charcoal’s surface matters.  Pore size is measured in microns; the smaller the micron measure, the finer the filtration and the larger the pore surface area there is.  Try to get a filter with a smaller pore size in order to get the most effective filter.

Pros and Cons of Having a Charcoal Water Filter

Before investing in a charcoal filter, be sure to check out the following reasons why you should and shouldn’t get one.

Pros of Charcoal Water Filters

  1. Easy to maintain: Charcoal filters require basically no maintenance.  When it’s time to replace it, all you need to do is switch out the existing filter with a new one.  
  2. Portable: For times when you’re out of the house and only have access to unfiltered tap water, charcoal filters come in handy.  You can purchase small charcoal filters that fit inside your typical water bottle.  They’re perfect for on-the-go lifestyles. 
  3. Keeps in the good minerals: Charcoal filters don’t filter out the healthy minerals in your water while getting rid of a lot of the bad stuff.  Minerals such as calcium and magnesium all pass through the charcoal giving the water higher dietary mineral content.  If you’re looking to up your mineral intake, switching to a charcoal filter could help. 
  4. Inexpensive: For those of us on a budget, charcoal filters are one of the most economical water filter options available.  Considering that they only need replacement after extended periods of time, they are highly cost-effective.
  5. No added chemicals: Many water filtration systems add chemicals to the water in order to disinfect it.  Charcoal filters are all-natural and do not add any chemicals to your drinking water.
  6. Reduces plastic consumption: Just about any water filter helps reduce plastic consumption by eliminating the need for plastic water bottles.  However, some water filters need to be changed constantly and are not recyclable.  To make it worse, they are also often made out of plastic.  Charcoal filters put little to no plastic back into the environment.  They are a fantastic, zero-waste waste solution!

charcoal water filter diy

Downsides of Charcoal Water Filters

  1. Deforestation: Despite the fact that charcoal filters help cut down on plastic use and are overall a more sustainable water filter option, there are some concerns about their impact on deforestation.  Wood needed to make charcoal has to come from somewhere and, recently, places such as the Amazon rainforest has experienced vast deforestation in part due to wood for charcoal.  Deforestation events such as these can throw off the entire ecosystem.  If you’re going to purchase a charcoal water filter, check first that you are buying a filter made of responsibly sourced materials.  
  2. Require additional filtration: Charcoal filters, unfortunately, aren’t able to filter everything that is bad out of water.  Particularly, the nitrites and microorganisms that slip through are of particular concern.  These are often the result of pollutants from farm feces runoff and herbicides 

Overall, charcoal water filters are a great option if you already have a sound and thorough system in your city or home that ensures the most dangerous contaminants are removed.  Charcoal filters act as a great second barrier to those contaminants that slip through the first round of purification.  

Make Your Own Charcoal Water Filter

Before purchasing a charcoal water filter, you can try making your own DIY one.  This is a great way to give it a test if you’re unsure whether purchasing one is worth it or not.  It’s also simple to do and makes for a fun activity!

What you’ll need:

  • 1 medium-sized mason jar
  • 1 plastic 2-liter bottle
  • Cooled, fresh charcoal
  • 1 large rock or iron gavel 
  • 1 small piece of fabric or 1 small handful of grass
  • 1 small handful of sand
  • Water

Directions:

  1. Cut the bottom end of the plastic bottle off
  2. Crush the charcoal on a flat surface using a rock or iron gavel until it is like a rocky powder
  3. Poke a small hole in the cap of the 2-liter bottle
  4. Place either a small piece of fabric or handful of grass in the 2-liter bottle near the cap
  5. Tightly pack the crushed charcoal on top of the fabric or grass and.  The 2-liter bottle should be about half filled up with charcoal.
  6. Place the handful of sand on top of the charcoal in the bottle.
  7. Place the 2-liter bottle cap down into the opening of the mason jar
  8. Slowly pour the water through the bottle (be careful not to pour it all on top at once)
  9. Once all the water has passed through the filter and is in the mason jar, run the process again until the water is clear (if the water is clear after the first time, then no need to filter a second time).
  10. Once the water is as clear as you’d like it to be, boil it at a rolling boil for at least 1 minute.
  11. Enjoy your freshly filtered water!

This homemade filter is also a great option for camping.  Be sure to boil your water after it has been filtered in order to get rid of microorganisms that passed through the charcoal!

Are Charcoal Filters Worth It?

Charcoal water filters are an economic, effective, and environmentally friendly way to help purify water. They are a great second safety measure you can take in addition to your existing water filtration system either in your city or home well. They’re definitely worth trying if you’re not completely satisfied with your water’s taste or cleanliness. 

Bonus tip: Check out our top picks for whole house water filters.  If you’re planning on trying out a charcoal filter, one of these filters will make a great first step to your water purification routine!

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Joshua Perkins

Joshua spent ten years as a water systems technician in California before settling down with his wife and two young children in Nashville in 2018. Through all of his experience, he learned the benefits and shortfalls of so many different types of water filtration systems, from pitchers to whole-house installations. He started Water Filter Authority in 2019 to empower other families to make the right decision for their long-term health and wellness.