Ask A Scientist

Why are we mostly made up of water? 

Asked by: Grace Merke
School: St. John the Evangelist
Grade: 5
Teacher: Anu Rai
Hobbies/Interests: Drawing, reading 
Career Interest: Dentist, vet 

 

Answer from Lina Begdache

Research Assistant Professor

Research area: Obesity, GERD, nutrigenomics
Interests/hobbies: running, reading

If a compound naturally exists in abundance in the human body, it means that it serves a major function. Water is no exception.

Water accounts for about 60-70 percent of our body weight. Men tend to have higher body water content due to greater muscle mass, compared to women who have more fat mass. A water molecule consists of one oxygen and two hydrogen atoms bound to each other by covalent bonds, which means that electrons are shared between atoms. Oxygen is more electronegative than hydrogen, which causes a stronger attraction of electrons. This is the reason why oxygen bears a negative charge. Since hydrogen is losing the electron, it bears a positive charge. Therefore, a water molecule is considered polar (two different charged poles) with the sum of these poles being neutral.

The polarity of a water molecule makes it a good candidate to attract regions of opposite charges in other molecules. Due to this chemical property, a water molecule is capable of performing so many functions in the human body. Some of the vital functions include:

• Acting as a main constituent of body fluids • Transport of nutrients and waste products • Assisting in chemical reactions and energy generation • Solvent for ions and other charged molecules • Lubricant for joints • Regulation of body temperature

It is worth noting that severe dehydration and water intoxication (drinking large amounts of water in a short period of time) can be fatal. Water is lost through respiration, sweat, feces and urine. Therefore, daily replenishment is needed. The Institute of Medicine recommends that women consume 91 oz. of water daily, while men should consume 125 oz. Fluid consumption could be in the form of water or water from food (e.g. soups, broth, fruits, juices). Note that caffeinated beverages such as coffee, tea and sodas are not good sources of hydration, as caffeine is a diuretic which increases loss of body water.

With temperatures rising, it’s especially important to stay hydrated. So fill up your cup and make it a fun, healthy summer. "Water" you waiting for?!  

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Last Updated: 9/25/14