"Set the basketball on the kitchen table. Open a cupboard, get out a bottle of sesame seeds, and place a single seed beside the basketball. If you were to reduce the Earth to the size of a basketball, all the fresh surface water on the planet - all those rivers and lakes and ponds and streams - would fit inside that one tiny sesame seed. Add a second sesame seed; now you have all the usable underground water as well. Is fresh water a scarce resource?"