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How much water do you really need?

Zelda Wilkinson, M.D.

Many articles in popular magazines have been telling people to increase the amount of water they drink every day. But how much do you really need, and how much is too much? 

Our bodies are about 60−70 percent water. Most of the water is actually in the cells themselves while the rest circulates around the cells and in the blood. We constantly are losing water which needs to be replaced daily.

How much do we lose, and where does it go? Most obviously we lose it in our urine. The kidneys are very efficient filters, and can process all of the body waste presented to them producing as little as 500cc of urine a day—that’s about 2 cups. We also lose a little water in our feces, more if there is diarrhea for any reason, and through our breath and skin. All total, the minimum amount of water lost daily is about 1400cc, one and a half quarts.

Of course, many circumstances can increase our need for water. Sweat is the most obvious, whether it is from increased temperature in the environment, increased exercise or both.

Sweat is basically salt water, so when there is excess sweating for whatever reason, salt as well as water may need to be replaced. This is the idea behind the various sports drinks. Most people doing regular exercise can replenish with plain water, but if you are training for a marathon or working outside when its 110 degrees, the electrolyte solutions such as Gatorade are probably a good idea.

Another circumstance that requires an increase in fluid intake is a history of kidney stones. The idea here is to keep the urine as dilute as possible to prevent the formation of stones. Also, if you have a bladder infection some doctors advise increasing fluid intake to help flush the bacteria out. Finally, if you are taking a fiber supplement a little extra fluid will help it work.

So, after all of this, how much do you need? As we saw above, this will vary with circumstances, but about a quart and a half is the minimal fluid requirement for most people with normally functioning kidneys. If it’s hot or you are exercising you’ll need more, and if you have a history of kidney stones you’ll need more. Fortunately, your kidneys can take most of what you pour into them, but the result will be an increase in the amount of urine you make.

How can you tell if you are not getting enough fluid?

Listen to your body; if you feel thirsty there is probably a reason! Concentrated urine is more yellow and darker than dilute, which is a sign of dehydration. Severe dehydration shows up as a dry mouth and poor skin turgor, which means the skin is stretchy and doesn’t bounce back when pinched.

Remember there is water in all fluids you drink and many foods you eat contain large amounts of water. That’s why they call it watermelon, right?  However, beer and other alcoholic beverages interfere with the action of a hormone that regulates urine production and actually causes you to produce more urine, which will defeat the purpose of hydration.

Finally, if you carefully monitor your body’s needs for hydration, it really doesn’t make sense to force yourself to drink eight glasses of water a day unless you need it for any of the reasons listed above. Key phrase—carefully monitor your body—don’t let dehydration sneak up on you!

Zelda Wilkinson, M.D., board certified internal medicine, earned her medical degree from University of Arizona College of Medicine in 1978. She has many years experience in Emergency Departments and dealing with dehydration issues. Dr. Wilkinson is on the Medical Staff at Verde Valley Medical Center. Her office location is 450 S. Willard Street, Suite 103, Cottonwood, phone 634-4231.