How to Make a Charcoal Water Filter

By: Jake Gallagher | August 23, 2023

In our quest for clean water, the age-old method of charcoal filtration (aka activated carbon filtration) often emerges as a trusted ally. What’s even better is that if you’re in a pinch, you can even make your own.

I know the water filter industry would have you believe you need the latest technology — and you do — water quality is pretty bad these days, after all. But emergencies happen, and you should know what to do if you’re in one.

Dive in to discover how to make your own water filtration system from charcoal and ensure you’re quenching your thirst with the purest water nature and science can offer.

How to Make a Charcoal Water Filter

Before you begin, it’s vital to choose the right material for safe water purification. While regular charcoal offers some basic filtration, activated charcoal, obtained through heating, excels due to its vast surface area. Grilling charcoal contains chemicals and should not be used.

Whether you’re going for regular or activated charcoal, the process of creating a filter remains largely similar. Here’s a more detailed breakdown:

Filter materials

  • Charcoal/activated charcoal: Purchased from health food stores, pet supply stores (often sold for fish tanks), online, or you can make your own
  • Sand: Both coarse and fine sand will be needed
  • Gravel: Small pebbles or stones
  • Plastic bottle or a similar container: The main body of the filter
  • Cloth or coffee filter: To prevent the finer materials from falling out of the filter
  • String or rubber bands: To secure the cloth or coffee filter

Step-by-step guide

1. Clean the components before assembly.

Before you start assembling your filter, make sure all components are clean. This includes the bottle, charcoal, sand, and gravel. Remember, you’re trying to remove impurities, not add them!

2. Prepare the charcoal. 

If you’ve purchased activated charcoal in granulated form, you might want to crush it slightly to increase its surface area. However, don’t pulverize it into a fine powder.

3. Prepare the container. 

Cut off the bottom of the plastic bottle and turn the bottle upside down (with the cap on).

4. Layer the filter.

  • First layer (top): Place the cloth or coffee filter over the neck of the bottle and secure it with a string or rubber band. This will prevent the finer materials from exiting the filter.
  • Second layer: Add a two-inch layer of coarse sand. This will catch larger particles and protect the activated charcoal from clogging.
  • Third layer: Add another two-inch layer, this time of fine sand. This finer sand will catch smaller particles that the coarse sand might miss.
  • Fourth layer: Add a three-inch layer of activated charcoal.
  • Fifth layer: Add a two- to three-inch layer of gravel. This layer aids in the removal of larger impurities and helps water flow more freely through the filter.

5. Use the filter

Pour water slowly into the filter, allowing it to drip through each layer. Collect the filtered water as it comes out from the bottom. It’s recommended to run the water through the filter more than once for better purification.

6. Maintenance

Over time, the activated charcoal water filter will become less effective as it gets saturated with impurities. When you notice a decrease in water quality or flow rate, it’s time to replace the activated charcoal. 

The sand and gravel layers can be rinsed and cleaned periodically. Washing a carbon filter might seem like a good way to extend its life, but it’s not recommended as it can dislodge the impurities trapped in the charcoal, reducing its effectiveness.

How to Make Activated Carbon at Home

Making activated carbon at home is a complex process that involves heating charcoal in a low-oxygen environment. While it’s possible to do, it’s generally safer and easier to buy pre-made activated charcoal.

But still, if you’re into chemistry and insist on giving it a try, here’s how you do it.

Filter materials

  • Hardwoods like oak, coconut shells, or sawdust are among the most common and effective materials. 
  • Burn your chosen material in a controlled environment, like a metal drum or a kiln, ensuring there’s limited oxygen.
  • Two ways to create activated carbon:

Chemical activation

  • This involves mixing the charcoal with a chemical, usually a strong acid, base, or salt. Common chemicals used include phosphoric acid, potassium hydroxide, or calcium chloride.
  • Once mixed, the combination is heated to a temperature of 450°–900°C (850°–1650°F). The chemical erodes the internal structure of the charcoal, increasing its internal surface area.
  • After heating, the charcoal is washed with distilled water to remove any residual chemicals, then dried.

Physical activation

  • This method involves heating the charcoal in the presence of a gas (like steam or air) to very high temperatures, between 600°–1200°C (1100°–2200°F).
  • The gas reacts with the charcoal, creating a porous internal structure and thus activating it.
  • Once activated, the carbon may need to be ground into a more usable form, depending on its intended application. For water filters, a coarse granular form is often ideal.

Safety precautions

  • Work in a well-ventilated area and avoid inhaling harmful fumes!
  • Handle chemicals with care! Wear protective gloves, eyewear, and clothing. Always follow safety guidelines and keep chemicals away from children and pets.
  • Ensure you have a reliable and accurate way to monitor the temperature to prevent accidents or over-burning.

What Is Activated Charcoal Filtration?

The primary mechanism by which carbon filters water is through adsorption. This is a process where molecules or particles adhere to the surface of another substance. 

Unlike absorption, where one substance is taken into another (like a sponge absorbing water), adsorption involves particles sticking to the surface.

Charcoal, due to its porous nature, has an extensive surface area relative to its size. This vast surface is filled with countless tiny pores and cavities, making it a magnet for various contaminants. 

When water passes over and through the charcoal, impurities in the water are attracted to the charcoal’s surface and get trapped, leaving the water cleaner as it exits the water filter.

The Marvels and Limits of Activated Charcoal in Water Filtration

Charcoal filtration is one of many, many types of drinking water filtration. As such, it has both its benefits and its drawbacks. After all, if there was one perfect method of water filtration, there’d only be one, wouldn’t there?

Adsorption power

Activated charcoal’s primary strength lies in its ability to adsorb a vast array of contaminants. But what exactly can it trap?

  • Organic compounds: Activated charcoal traps many pollutants and contaminants found in water sources(including pesticides, herbicides, and industrial solvents)
  • Chlorine and chloramines: Many municipal water treatment facilities use chlorine or chloramines to disinfect water. 
  • Heavy metals: Metals like lead, mercury, and copper can find their way into water sources due to industrial processes, old plumbing, or natural deposits. 
  • Certain bacteria: While not its primary function, activated charcoal can trap some bacteria types, preventing them from passing through the water filter. However, it’s essential to note that this isn’t a foolproof method of bacterial removal.

Economical and eco-friendly

While activated charcoal can be a bit pricier than regular charcoal, it’s still a cost-effective option compared to many commercial filters. 

Additionally, it’s a pretty eco-friendly filtration method. All materials involved in the process are natural, and used activated charcoal can be composted.

But limited filtration ability

  • Viruses: Viruses are much smaller than bacteria and are not effectively adsorbed by activated charcoal. If viral contamination is a concern, additional purification steps are necessary.
  • Hard minerals: Minerals that cause water hardness, like calcium and magnesium, aren’t effectively removed by activated charcoal. If you’re looking to soften your water, you’ll need a dedicated water softener.
  • Saltwater desalination: Unfortunately, activated charcoal can’t remove salt from water. Desalination requires more advanced methods like reverse osmosis.

Other DIY Charcoal Filters 

The method described above may not be practical for every scenario. In case your supplies or situation is limited, here are some other ways to filter water using activated charcoal.

Survival charcoal water filter

This one is similar to the method above but for situations with limited supplies.

How to make it

  1. Gather materials. You’ll need a plastic bottle, charcoal (preferably from hardwood), a cloth or coffee filter, and a string or rubber band.
  2. Preparation. Cut the bottom off the plastic bottle and place the cloth or coffee filter over the neck, securing it with the string.
  3. Layering. Fill the bottle with crushed charcoal, ensuring there’s enough to effectively filter the water.
  4. Usage. Pour water through the top and collect the filtered water from the neck.


  • Portability: It’s lightweight and easy to carry.
  • Simplicity: Requires minimal materials and can be set up quickly.

DIY water filter with charcoal and sand

For a more advanced water filtration system, combining charcoal with sand can offer enhanced purification. With this one, however, you’ll need access to a tap or spigot.

How to make it

  1. Gather materials: You’ll need a larger container (like a bucket), gravel, sand, charcoal, and a spigot or tap.
  2. Layering: Start with a layer of gravel at the bottom, followed by sand, and then charcoal. Each layer should be several inches thick.
  3. Installation: Install the spigot or tap a few inches above the bottom of the container. This ensures you’re drawing water that has passed through all the layers.
  4. Usage: Pour water into the top of the container and collect the filtered water from the spigot.


  • Enhanced filtration: The sand layer can trap smaller particles that charcoal might miss.
  • Higher volume: Suitable for filtering larger quantities of water.

Important Notes

  • Boiling: While the activated charcoal filter will remove many impurities, it won’t kill pathogens. Always boil the filtered water for at least 10 minutes to ensure it’s safe to drink.
  • Storage: Store unused activated charcoal in a dry place to prevent it from losing its adsorptive properties.
  • Layer thickness: Depending on the size of your container and the amount of water you wish to filter, you can adjust the thickness of each layer. However, ensure that each layer is thick enough to serve its purpose effectively.


Charcoal, in its various forms, remains a trusted ally in natural water purification. Whether you opt for regular wood charcoal or the superior activated type, understanding their roles is key. 

Crafting a DIY filter is not only feasible but also a testament to the blend of nature and innovation. As we seek purity in every drop, charcoal filtration stands as a reliable and sustainable choice. 

Clean water is more than clarity; it’s about ensuring safety with every sip.


Can you make your own charcoal water filter?

Yes, you can craft your own charcoal water filter using basic materials like untreated charcoal, sand, and gravel.

How do you make a homemade charcoal filter?

Start with a container, layer the bottom with gravel, followed by sand, and then add untreated charcoal on top. Pour water through the top and collect the filtered water from the bottom.

What kind of charcoal do you use to filter water?

For water filtration, it’s best to use activated charcoal due to its enhanced adsorption capabilities. However, untreated hardwood charcoal can also be used.

Can you use wood charcoal to filter water?

Yes, wood charcoal can be used for basic filtration, but ensure it’s natural and free from any additives or treatments. For optimal results, activated charcoal is recommended.

Interested in knowing more about water filters? Explore their importance in upholding a reliable water supply with these additional resources: