Even IF the earth was flat, to the person that believes
the earth is round, "down" is always toward the center
of the earth, so everything (including water) will flow
'downhill' locally but can and does 'bend around the planet'
because at each point, it IS at the lowest level.

Are you too thick to understand that this is fully consistent
with a round-earth model of reality?  And that you cannot
disprove that model by pointing out that an aspect of
it doesn't jive with YOUR model of reality?

I wouldn't expect you to be that intelligent, but try
thinking about it.