The atoms
So far we have regarded
each water molecule
as an autonomous entity
which experiences
its "adventures" undivided.
It may actually
be that ever since
the material of the
earth was cooled off,
a water molecule which is then formed
is left intact after four and a half billion
years and merely changed its place.
One time in the atmosphere, another time
in a glacier, and another time in a cell in
the body of a dinosaur.
But it may
be that chemistry played a part to.
It may have been
split for example during photosynthesis
(which dissociates
a large quantity of water each year)
and later have been re-formed by combustion.
Not necessarily from
the same atoms which were originally
joined but from
other hydrogen atoms each of which
has its own "history" and an oxygen atom that perhaps
never until now was in a water molecule.
Since chemistry
interferes
it would be even more
correct if we consider
the atoms as the fundamental components
of our droplet
so that
we can follow the story back
to the beginning, to the Big Bang.