actually I have a similar question what happens if someone -breaks wind and you breathe it in -do you breathe it out all over someone else or does your body store it ! ! !
I have had a very believable answer from a doctor -But
There's only so much water on the planet. It washes away, it evaporates, it rises to form clouds, it falls as rain, the cycle starts again. Every drop of water has been drunk exactly 23 billionty gazillion times. Bit late to start worrying now.