The bottom line is that water kefir NEVER goes bad. If it is in a sealed bottle with no chance of cross contamination, the LIVE cultures will slowly continue to eat up the sugars in the drink and eventually the drink will turn to vinegar.
Water kefir has a very low Ph. We transfer it to the jugs and bottle it when it reaches a level of 4.0-4.3
The first ferment with no flavoring added can last in the fridge for up to 3 months. The LIVE cultures in the drink slowly continue to eat up the sugars but it is very slow. As I mentioned, it eventually turns to vinegar.
The second ferment soda version usually only lasts up to 2 months in the refrigerator because of the added flavor. The LIVE cultures love the added sugar and eat it up quicker. Some flavorings like lemon last longer in the fridge because of the low sugar content but I find the sweetness of cherry goes to vinegar much quicker.