ABSTRACT
When we speak of water and its many manifestations, we are speaking of that endless quintessential cycle that predates all other cycles. Water is our most precious natural resource; we can’t survive without it. There is no more water today than there was yesterday-that is, no more this year than there was 100 million years ago. The water present today is the same water used by all the animals that ever lived, by cave dwellers, Caesar, Cleopatra, Christ, da Vinci, John Snow, Teddy Roosevelt, and the rest of us-again, there is not one drop more or one drop less of water than there has always been. This life-giving cycle, a unique blend of thermal and mechanical aspects, is dependent on solar energy and gravity (see Figure 4.1) for its existence. Nothing on Earth is truly infinite in supply, but the energy available from water sources, in practical terms, comes closest to that ideal (Spellman, 2008).
