Upgrade any* bottle to a filter bottle. This stainless steel coil securely holds the 100% natural active charcoal filter, with no rattle and no scratches! Simply put the charcoal into your water, we recommend one stick per litre, then leave for 1 hour (8 is best) and enjoy your filtered water. Each charcoal will last for 6 months as a water filter, simply recharge after the first 3 months use. *Minimum spout width of 30mm. About Black+Blum : Black+Blum are award-winning producers of original, sustainable products that people love to use every day and are proud to own. They endeavour to create objects of enduring value and practicality that age well and are built to last.. Dan Black and Martin Blum are passionate about sustainability and doing their part to protect the environment. They have an eclectic taste and this shows through the varying aesthetics of their individual products. They design in-house but also collaborate with the most talented designers worldwide to bring the finest lunch boxes and water bottles to the market. Upgrade any bottle to a filter bottle. This stainless steel coil securely holds the 100% natural active charcoal filter, with no rattle and no scratches!