Plain or Peanut?

I watched a very interesting short video from Worldviews Network today, "A Global Water Story." I learned a lot about fresh water and how it's in increasing demand around the world, even as climate change makes dry areas drier and wet areas wetter and ancient underground aquifers sink rapidly. To set the scene, the video uses a clever analogy to show how little of our planet's water is fresh water. 

Imagine that all the water in the world is represented by a one gallon (3.8 liter) pitcher. All of this would be salt water except for three shot glasses of fresh water (a shot glass holds about 1.5 fl. oz. or 44 ml). The contents of two of the three shot glasses would be frozen polar ice. Of the fresh liquid water in the third glass, most of it would be underground. The drinkable amount available on the Earth's surface would be the volume of a single M&M candy (a volume of about 0.64 cm^3 or 0.64 ml):