If all the water on earth is represented by 1000-L tank how many millilitres of that would represent potable water?

If all the water on Earth is represented by a 1000-L tank, only about 2.5% of that is freshwater, and only a small fraction of that is accessible and safe for drinking (potable water). This amounts to roughly 25 L of freshwater, but only about 1% of that is readily available for human use, which is approximately 0.25 L or 250 mL. Therefore, in this analogy, potable water would represent about 250 mL of the 1000-L tank.