How often should you replace SodaStream CO2 cylinders?

According to the SodaStream website, users need to replace the machine's CO2 cylinders when they are empty and can no longer carbonate water. The length of time for a typical CO2 cylinder to empty varies according to how much soda a household consumes regularly.

As of 2015, SodaStream offers CO2 cylinders that carbonate an average of 60 or 130 liters. These cylinders do not have an expiration date and last indefinitely as long as users store them properly. SodaStream also recommends that users refill any empty CO2 cylinders at SodaStream, as local or third-party filling stations may not have beverage-grade CO2.