How does charcoal filter water?

The history of binchotan charcoal, how it works and what you can do with it.

Black and blum active charcoal water filters on a grey bench with eau good reusable charcoal water bottle.

Sometimes referred to as ‘white charcoal’, this incredible natural material was thought to have been introduced to Japan by Kukai, a Japanese monk and scholar, about 1,200 years ago. However, it wasn’t until the 17th century that it became popular thanks to Bichuya Chozaemon, hence the name more commonly used today, “binchotan”.

We first identified binchotan charcoal being used in Japan about 10 years ago, and were inspired to design a reusable water bottle which could incorporate this kind of unique filtration. We knew it would resonate with a western audience, particularly in cities like London where the tap water tastes heavily chlorinated. We wanted to find a solution which could replace the need for single-use bottled water, which we know is massive contributor to plastic waste, but also a major carbon emitter in terms of it’s production. It’s also very difficult to find a water filter which doesn’t require any hard plastic casing in order to filter effectively. And so our iconic Eau Good water bottle was created, and due to it’s success, we’ve since expanded to an entire range of charcoal filtration products.

How is it made?

Making binchotan charcoal requires a very fast rise in temperature, and then rapid cooling, which leaves a hard and smooth surface. If you tap it, you’ll hear a clear, metallic sound.

We source our charcoal in Laos from producers who only prune the branches of their fast-growing native trees, without removing the roots. This means the trees can grow back, and be collected again, in 5-year rotations. The wood is harvested local to their kilns and this ensures the forests where the wood grows are protected.

The process to create binchotan charcoal follows the ancient Japanese process. It involves charring wood at a low temperature in a kiln for a long time. Just before it’s finished, the temperature suddenly is increased to about 1000°C (1800°F) until the wood is red hot. A special powder is then created by combing earth, ash and sand, and this is used to quickly cover the charcoal once it’s removed from the kiln.

Binchotan charcoal removed from kiln and covered with a powder of earth, ash and sand to rapidly cool it

This process is what gives the charcoal a white hue (which is why it’s referred to as ‘white charcoal’).

Binchotan active charcoal water filters cooling after burning in a kiln.

The charcoal pieces are then pressure washed, vacuum sealed and shipped to our distribution centres all over the world.

Black and blum active charcoal water filters on a marble bench

How does it work?

Black and blum binchotan active charcoal water filter bottle working to filter tap water

Binchotan charcoal has an incredibly porous surface with tiny cavities oriented in many directions. Just 1 gram has a surface area in excess of 500mᒾ (about one-tenth the size of a football field). All of these cavities provide areas where the charcoal can draw in and absorb contaminants in your drinking water. It known as ‘active carbon’ as the negative ions of contaminants are attracted to the surface of the carbon, where they will be trapped.

Binchotan charcoal is also able to release minerals such as calcium, iron and magnesium back into the water which enhances its taste and health benefits.

How long does charcoal last to filter water?

They last for 6 months, however, if you’re using them every day to filter about 1.1L (37 fl oz) of water, it’s important to recharge your charcoal half way through (usually at about 3 months). It also depends on things like the quality of your drinking water, and how many charcoal sticks you use (for example you could have a water dispenser that uses 4 charcoal sticks at a time). Generally judging charcoal effectiveness by taste is a reasonable way to understand if it’s time to recharge your charcoal. However, in our experience, the 3 month-mark is usually correct.

Once your charcoal has been recharged, you can use for another 3 months. Not sure how to recharge your charcoal? Follow our handy guide here.

Black and blum active charcoal water filters being used in a water dispenser.
Image: 4-pack Active Charcoal filters from Black+Blum being used in a water dispenser.

Secondary uses of binchotan charcoal

At Black+Blum, we’re big believers in the circular economy, so we love to find afterlife and secondary uses for our products. This means less reasons to buy more, and less waste going to landfill.

Binchotan charcoal really is a miraculous material. Once it’s finished its life as a water filter, it can be used all around the house and garden. And, unlike other charcoal filters available, it contains no plastic casing or cover, so it can go straight from your bottle back into the environment.

Active charcoal water filters being used in a fruit bowl

Keeps fruit fresher for longer

When fruit begins to ripen, it releases a gas called ethylene, which can make other fruits ripen around it. Adding active charcoal to your fruit bowl can help slow this process, as it can absorb ethylene the same way it absorbs the chlorine in your water.


Active charcoal water filters being used in the soil of a plant pot

Gives your plants a boost

Binchotan charcoal helps release minerals like potassium into your drinking water, so in the same way, it can help plants to absorb additional nutrients from the soil so that they stay healthy and green.

Simply break it up (you might need a hammer!) and add to the soil.


Active charcoal water filters in an old pair of white shoes.

Deodoriser + dehumidifier

It works by drawing and binding contaminants to its surface – and it can be really useful for absorbing moisture and bad smells.

Perfect to pop in your clothes drawer to keep damp away, or even in a cat litter. It also works well to draw in moisture from the fresh fruit and vegetable drawer in your fridge.

Our binchotan water filters can be used in any water vessel, including different reusable water bottles, but also jugs and dispensers. We have an extensive range of charcoal filtration bottles, accessories and carafes.

Designed in London. Made to Last.

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