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H2O – It’s Your Most Important Nutrient

Written by: Cindi Lockhart, RD, LD, Weight Loss Coaching Program Manager

Water makes up about 70% of our brain, 85% of our blood, 90% of our lungs, 75% of our muscle, and 10% of our body fat.  Knowing this difference in composition between muscle and body fat explains why adult men are higher in water content (60%) than adult women (55%), since women store more fat than men do.[i] 

It’s estimated that 75% of Americans are chronically dehydrated with 100% of these being preventable. We will be discussing the health benefits of water, symptoms of dehydration, how much water we need to drink, differences between sources of water, and practical tips on how to increase water intake.

Because our bodies are primarily water, adequate hydration is essential for energy, nutrient absorption and improved digestion, maintaining body temperature, detoxification (flushes the kidneys and digestive tract), easing joint pain (lubricates the joints), optimal mental function (focus, memory, concentration), younger appearance (hydrates the skin), plus weight control. 

The University of Washington found that mild dehydration decreases metabolism by 3%.[ii]  With regard to energy, the number one reason for daytime fatigue is dehydration. Consider how difficult it is for your heart and lungs to push nutrients and oxygen (energy) through our cells. A 2005 study found proper hydration decreased blood viscosity in heart disease, dilute toxins in cancer, and cleanse the airways in asthma.[iii]

During the course of a normal day, it is thought that a normal adult loses up to 10 cups of water via breathing, urinating, and sweating alone. This does not include exercise!  Some symptoms of mild dehydration include thirst, decreased appetite, fatigue, headaches, dry mouth, constipation, and dizziness upon standing. With more severe dehydration, one may experience extreme thirst, irritability, confusion, lack of sweating, sunken eyes, no urination, rapid heartbeat and breathing.ii  

Thirst, itself, is not an accurate measure of water needs. If you feel thirsty, you are already clinically dehydrated.  The American College of Sports Medicine (ACSM) suggests a 2 percent loss of body water negatively impacts fitness performance by 15-20 percent.[iv] 

So how much should we be drinking each day?  No science or research exists to confirm the long-held recommendation of drinking eight 8-ounce glasses of water daily.  Newer thought points to drinking half our body weight in water ounces per day (ex: a 150-pound woman should drink 75 ounces of water daily) to optimally hydrate, energize, and detoxify.  Add another two cups of water per hour of exercise to replace the fluids lost via sweat and respiration. The Institute of Medicine recommends adult men drink at least 13 cups of water per day and adult women to drink at least 9 cups. It is also suggested we monitor our urine color — with adequate hydration, it should be clear to pale yellow. 

On the flip side, what are the risks of drinking too much water?  Drinking more than the body needs to function can dilute the blood sodium level, a condition called hyponatremia or water intoxification.  If left untreated, it can disrupt neurological function, cause a heart attack or even death.    

What source of water is the best: tap, filtered, or bottled?

Tap water

Depending on where you live, the E.P.A. has found lead, chlorine, bacteria/microorganisms, mercury, industrial chemicals, disinfectants, and even radionuclides in our tap water.[v]  As a result of contamination, the National Resources Defense Council (N.R.D.C.) cautions pregnant women, young children, elderly, and those with weakened immune systems against drinking tap water due to the risks imposed.[vi]  The Fluoride Action Network is concerned with excess fluoridation in tap water as it can discolor children’s teeth, weaken bones, cause eczema, suppress thyroid function, and affect mental function (I.Q., learning, memory).[vii]  It is a good idea to get a copy of your city’s annual water quality report to know what’s in your water. 

Bottled water

Are water bottles better? The N.R.D.C. states 25-30% of bottled waters are from tap water sources. You can identify this when the label states, “from municipal source” or “from community water system”.[viii]  Bottles are also required to be tested less than tap water with F.D.A. rules allowing for some bacterial   

As well, chemicals such as Bisphenol-A (B.P.A.s) and phthalates are found in plastic bottles. Over time and with exposure to extremes in temperature, these chemicals degrade and leach into the water. Known as environmental or estrogens, or xenoestrogens, such compounds can disrupt sex hormone balance. And there is no legal limit for the amount of “foreign” chemicals in our bottled waters. 

Note that plastic bottles labeled #7 PC contain B.P.A.s, and those labeled #1 and #2 are subject to bacteria and should be washed with warm water after every use.

Filtered water

What about filtration?  One of the safest water filtration systems found is Reverse Osmosis (R.O.). This process purifies water by removing several minerals, contaminants, heavy metals, iron, fluoride, and arsenic.[ix]  There are household-wide R.O. filtration systems, cooking options (you can often lease a system via a local water company) and kitchen sink options for just drinking. As well, several of the most popular bottled waters are filtered via R.O. today. 

So, if plastic is not your choice, your best options are to drink water from glasses (real glass) or stainless steel bottles. Be cautious of aluminum bottles, which can disrupt neurological functioning and health. They should contain a liner that does not include B.P.A.s.

Now that we know the importance of water and the sources that are healthiest for us, let’s look at some ways to help us increase our daily intake:

  • Set a phone or computer reminder to remind you to drink more during the day.
  • Buy a new colorful stainless steel bottle to inspire your new habit.
  • Start carrying your glass or bottle of water with you, wherever you are – when you rise in the morning, are driving to work, at your desk, while exercising,  throughout errands, and up until bed.
  • For a little change of flavor, try adding a slice of lemon, lime, orange, or cucumber to your water.

Get in the H2O habit today!

This article is not intended for the treatment or prevention of disease, nor as a substitute for medical treatment, nor as an alternative to medical advice. Use of recommendations in this and other articles is at the choice and risk of the reader.



[ii] Batmanghejidj, F. (2008)  Your body’s many cries for water. Global Health Solutions, Inc., 3rd ed.

[iii] Yun, AJ et al. “Clinical benefits of hydration and volume expansion in a wide range of illnesses may be attributable to reduction of sympatho-vagal ratio”. Med Hypotheses. 2005; 64 (3): 646-50.

[iv] ACSM position statement. Eat to fuel your performance, 1997.





[ix] www.EWG,org

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