Good question! Our carbonating bottles are made to withstand extreme pressure changes when used for carbonation, and since plastic degrades over time they sadly can't be used forever. Note the expiration date printed on the bottle and be sure to purchase new bottles as soon as the original bottles expire. The plastic bottles must also be replaced if put in the dishwasher, exposed to a heat source, or if they have become scratched. The good news is that all components of carbonating bottles except for the seal inside the cap are recyclable. Please check with your local recycling authority for more information on sustainable disposal options.