Black+Blum Charcoal Refill Water Filter - 3 Pack Binchotan charcoal is an active carbon made from tree branches It absorbs impurities such as chlorine by attracting the negative ions to its surface In exchange, the charcoal sends its nutrients (calcium, iron and magnesium) back into the water It also neutralises the water's pH levels Each stick lasts for 3 months; At this time if you boil it in water for 10 minutes it will recharge for a further 3 months