glass of water1. Our sweat evaporates invisibly through pores.
2. Sinking air pushes on drained, shrunken cells.
3. If you don’t drink enough H2O (or overdo caffeine and alcohol which drain water out), all kinds of dehydration ailments appear because of weakened circulation and immune systems (coughing, aches, exhaustion, stress hunger, concentrated hormones & sex drive, joint pain, forgetfulness, etc.). Water is the conduit for our brains, blood, lymph, lung tissues, electricity, muscles, GI tract (digestion), etc.

Just try an experiment. If you feel tired and achey, start drinking water at a rate you can absorb it, not bloat.

Fat also needs water to metabolize. I lost 25 lbs. when I grasped this, and though not perfectly fit of course,  have kept it off 6 years.
Los_Angeles_Basin, wikipedia image