system
Given the following post, respond as if you're commenting on Reddit:
human
How old is the water we drink?

We are taught that matter is never created nor destroyed, but rather it just changes forms.   For example: plants grow and animals eat them.  The animals eventually die, decompose, and become part of the soil on which new plants grow again.  

What about water?  What is the average age of our tap water (from the time that the matter which makes up the water was something else)?   Does the matter which is our tap water generally just exist (and has existed) as water?  Or do parts of other matter get converted to water as part of some life's cycle?
gpt
Water can be destroyed.  In photosynthesis the oxygen is split off and released.  In the upper atmosphere it is dissociated into hydrogen and oxygen and much of the hydrogen escapes into space.  What is mostly constant is the hydrogen, much of which dates from the time of the big bang, and the oxygen, which was formed within stars at the same time as most of the elements n Earth.