That’s how much water I’m walking around with in my body mass.  Imagine carrying 120 pounds of water –that’s three nearly full 5-gallon water jugs — around with you all day long, every day of the year. No wonder I’m so tired at the end of the day. You can do this math for yourself.  An average adult’s body is 60-70% water; for children it’s closer to 75% but it can get as low as 45% if you’re overweight. Take your body weight and multiply it by the appropriate percentage of water and you’ll see how many pounds of water you’re packing.  If you want to convert those pounds of water into gallons, just multiply by 8.4. Add another 24 pounds of skin and what you’ve basically got is hundreds of thousands of years of human evolution producing an ambulatory water balloon wrapped in flesh. University of Chicago scientist Neil Shubin writes in his book Inner Fish that we hiccup because of a design malfunction in our nervous system and a breathing apparatus passed down from fish and tadpoles.  It appears that when our animal ancestors crawled out of the ocean they somehow forgot to purge their water ballast as well. Fortunately, we also have a three-pound brain that can tell our body balloon where to go.  How to fall in love.  How to launch fellow balloons into space. Before your brilliant cerebral cortex starts thinking that dehydrating yourself would be a smart diet plan, I’ll caution you that our highly evolved body balloons run on a very thin tolerance for water loss. During a normal day, we breathe, pee, and sweat out about three quarts of water, amounting to 5-10% of our body’s water. Note that if you’re running the 150-mile Marathon Des Sables across the Saharan Desert in Morocco, you’re likely leaking more than 12 quarts a day.  If you’re not continuously replenishing your body’s water you can run into trouble in a hurry. With a deficit of as little as one quart you’re likely going to start losing some cognitive function, alertness, and ability to concentrate.  If you lose a gallon you’ll start feeling pretty lethargic, and you’ll likely have a bad headache.  If you’re down two gallons you’re going to be sick enough to be in the hospital.  Three gallons and you’re in the morgue. Yet our water needs are so much greater than simply keeping our bodies hydrated, and therein lies the great water challenge of the 21st century.  We use water to grow our food, generate our electricity, and manufacture our clothes.  If you visit National Geographic’s Water Footprint Calculator you’ll see that it takes about 2,000 gallons of water per person each day to support an American lifestyle.  That places a lot of strain on the freshwater systems of our planet, a theme that I’ll return to repeatedly in the coming weeks and months in my Water Currents blogs. Water is at the very core of our being.  John Muir once said, “The rivers flow not past, but through us.”