A long time ago, I learned I could use my campfire charcoal to filter any questionable water sources if no other water was available. Not surprisingly, charcoal can have a profound effect on softening ordinary tap water, too.

London-based design firm Black+Blum recently designed an interesting (BPA free) water bottle to take advantage of a specific type of charcoal called Binchotan, which has been used for cooking and filtering water since the Edo period (1603).

The secret of the charcoal is its ability to soften water, add minerals such as calcium, potassium, and magnesium and absorb certain chemicals such as chlorine. It accomplishes this due to the numerous tiny pores scattered all over its surface area, which attract the positive ions found in some contaminants. Those contaminants stay locked in the carbon, allowing it to filter water for a lifespan of around six months and then can be recharged just by boiling it in water for an hour or more.

While you can use Binchotan in any container, Black+Blum have designed a modern polymer bottle, known as the Eau Good Duo, which allows you to lock the charcoal in place—rather than have it float loosely—and locks by merely squeezing the bottle’s sides. They’ve also included an infuser cap; allowing users to put fruit and herbs in the container that won’t make you feel like you’re eating a salad every time you take a sip. The bottle also features a leak-proof cap that functions much like push/pull spout tops found on many water bottles, although Black+Blum’s design is more robust and made out of sturdy rubber.

Black+Blum is currently crowd-funding their Eau Good Dou bottle on Kickstarter, and those looking to get their hands on one can pledge $31 or more, which nets you the bottle plus one Binchotan filter (you get more with higher pledges).

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