Hydration is important in order for your body to function properly and for it to function at optimal levels during activities like exercise. We can live without food for weeks but within a few days of no water or hydration your entire body begins to shut down. I know when I am adequately hydrated I function better both physically and mentally. When I don't drink enough water or fluid I get cranky and usually develop a terrible headache. My drink of choice is water with unsweetened seltzer ...