The lifespan of a Cirkul flavor cartridge depends on several factors, such as the frequency of use, the flavor strength, and personal preferences. On average, a single flavor cartridge can last for up to 15 refills, which is equivalent to around 15-20 liters of water. However, some users may find that they need to replace the cartridge more frequently, while others may find that it lasts longer. Cirkul offers a subscription service that makes it easy to order new cartridges as needed.