http://www.eatingwell.com/nutrition_health/nutrition_news_information/why_drink_water
By Rachael Moeller Gorman, "Liquid Assets,"July/August 2011
Water accounts for 60 percent of our body—or about 11 gallons or 92 pounds inside a 155-pound person—and is essential to every cell. We use water to cool our body with sweat, to circulate oxygen and fuel to our organs and take away waste products via blood. But how does it impact your breath, muscles, skin—and brain function? Find out here.
Next: How Being Hydrated Affects Your Brain » [pagebreak] BrainStaying hydrated keeps your memory sharp, your mood stable and your motivation intact. When you’re well-hydrated, you can also think through a problem more easily. Researchers hypothesize that not having enough water could reduce oxygen flow to the brain or temporarily shrink neurons—or being thirsty could simply distract you.
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Next: How Being Hydrated Affects Your Mouth » [pagebreak] MouthWater keeps your throat and lips moist and prevents your mouth from feeling dry. Dry mouth can cause bad breath and/or an unpleasant taste—and can even promote cavities.
Next: How Being Hydrated Affects Your Heart » [pagebreak] HeartDehydration lowers your blood volume, so your heart must work harder to pump the reduced amount of blood and get enough oxygen to your cells, which makes everyday activities like walking up stairs—as well as exercise—more difficult.
Next: How Being Hydrated Affects Your Bloodstream » [pagebreak] BloodstreamYour body releases heat by expanding blood vessels close to the skin’s surface (this is why your face gets red during exercise), resulting in more blood flow and more heat dissipated into the air. When you’re dehydrated, however, it takes a higher environmental temperature to trigger blood vessels to widen, so you stay hotter.
Next: How Being Hydrated Affects Your Limbs » [pagebreak] LimbsWhen you’re well hydrated, the water inside and outside the cells of contracting muscles provides adequate nutrients and removes waste efficiently so you perform better. Water is also important for lubricating joints. Contrary to popular belief, muscle cramps do not appear to be related to dehydration, but, instead, to muscle fatigue, according to Sam Cheuvront, Ph.D., an exercise physiologist for the U.S. Army Research Institute of Environmental Medicine.
Next: How Being Hydrated Affects Your Skin » [pagebreak] SkinWhen a person is severely dehydrated, skin is less elastic. This is different than dry skin, which is usually the result of soap, hot water and exposure to dry air. And, no, unfortunately, drinking lots of water won’t prevent wrinkles.
Next: How Being Hydrated Affects Your Kidneys » [pagebreak] KidneysYour kidneys need water to filter waste from the blood and excrete it in urine. Keeping hydrated may also help prevent urinary tract infections and kidney stones. If you are severely dehydrated, your kidneys may stop working, causing toxins to build up in your body.