Someone reckoned that the whole population of the earth would fit into the area of California. (1 sq m per person - yes, pretty sqeeezy)
But shoulder to shoulder, we would fit into the area of Los Angeles.
That probably puts into perspective how much water there is stored in the human population.
http://news.nationalgeographic.com/news/2011/10/111031-population-7-billion-earth-world-un-seven/
