This membrane is the replacement filter for our foldable water bottle. (A membrane filter is already included in your HumaGreen bottle) It has a lifespan of around 1000L, or more than 1 year with a consumption of 2L of water per day. How do I know if my current membrane has expired? You simply won't be able to suck water through it anymore. First try blowing into the bottle to expel the unsuitable water, then try to vacuum again. If this does not work, then the membrane needs to be changed.