Water is the first thing scientists look for when attempting to deem a location (say, a far off planet), potentially hospitable for life.

It’s possible to live a few weeks without food.  Gandhi fasted 21 days, and Irish prisoner Bobby Sands went 66 days on a hunger strike before he died. After large scale disasters, it’s not unusual to hear of someone who lived under rubble for even a few weeks–as long as they had access to water.

But without water? NBC News quotes Duke University Professor Dr. Pitandosi describing a 100-hour rule: at average outdoor temperatures, sheltered from the sun and not moving around, a hydrated adult can survive about 100 hours without drinking. Try this in a place like Bakersfield, where summer temps soar above 100 degrees, and the 100-hour rule goes right out the window.

The Dietary Reference Intake (DRI) for water is 91 oz per day for women and 125 oz per day for men. This includes all water consumed from food and beverages; on average, 20% of one’s daily water intake comes from food and the rest is from beverages.

Of Course, Water is Important.  But Why Exactly?

It’s probably not news to you that you ought to drink plenty of clean water each day. But what exactly is the purpose of water in the body?

Some of water’s functions are familiar:  It makes up tears, mucus and saliva, flushes water soluble wastes out through the kidneys as urine, and helps to regulate body temperature via perspiration and insulation.

But did you know that on average 60% of your body is water?  Babies actually start at about 75% water, and we tend to dry out as we age, with females retaining less water than males starting at puberty. Obese individuals also carry less water than their lean counterparts. Water makes up most of your vital organs:  In 1953 H. H. Mitchell determined via desiccation studies that, on average, the brain and heart are 73% water, the lungs are 83%, muscles and kidneys are 79% water, and even bones are 31% water!  

All the “wet” stuff in your body comes from water: joint lubrication; the shock-absorbing fluid surrounding the brain and spinal cord; digestive fluids and other secretions.

Beyond saliva, water is involved in digestion when hydrolysis reactions take place, breaking proteins, fat and carbohydrates down into basic elements useful to the body.  Then, water helps deliver minerals, trace elements and water soluble vitamins to the cells. At the other end of the digestive process, water helps to keep stools soft and easy to eliminate.

Blood is more than 50% water. (Blood is 55% plasma, which is 92% water; the remaining 45% is mostly cellular, but cells also contain water..)

Water keeps the concentration of the various elements in your body at the right dilutions.  Situations where certain minerals such as sodium and potassium are too concentrated or too dilute are life threatening; the right concentration is vital to nerve conduction and cell reproduction.  

Although we’re not totally sure why, drinking water improves mental reaction rates.  Your brain needs water for making hormones and neurotransmitters.

Digestion. Detoxification. Depuration. Temperature regulation. Structural support and protection. Nerve function.  It’s no wonder we sound like a broken record talking about water here. And here. And here. And here. And here.

What do you notice when you don’t drink enough water?

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