While petroleum was the dominant natural resource influencing world events throughout the 20th century, by most indications, the one poised to usurp its position in the 21st – to be the source of geopolitical conflict and unrestrained economic exploitation – is water. While you’re mulling that one over, consider as well just how much you actually know about it. If you’re like most people, you’ve likely not given it much thought beyond secondary school science classes.