When you skimp on fluids, it’s hard on your body, which makes sense because water is essential to just about every process in our body and, in fact, to the very existence of life on Earth. Life first emerged in the salty, primordial ocean; it stayed there until it was able to capture a bit of that water inside itself, the so-called “milieu intérieur” in which cells are bathed. Our inner ocean is a calm, salty broth providing cells with the raw materials they need to function, removing waste products, allowing them to communicate with each other and buffering them from the unpredictable world outside.

Water accounts for about 60 percent of our body—that’s about 11 gallons, or 92 pounds, inside a 155-pound person. Most of it lurks inside our cells (where all sorts of important substances are dissolved in water) and outside them (the milieu intérieur), but we also use it to cool our body with sweat, to circulate oxygen and to fuel our organs, and to take away waste products via the blood. The elderly, infants and sick children are most prone to dehydration, but no one is risk-free. If you’re really busy, it’s easy for the morning to fly by and you don’t realize you’ve had nothing to drink until you notice you are thirsty, at which point you’re already slightly dehydrated. And when you engage in strenuous exercise, such as playing soccer or football or running distances in the summer and forget to hydrate, you can easily lose 4 to 5 percent of your body weight.

Three simple questions can determine if you’re dehydrated: Am I thirsty?  Is my morning urine dark yellow?  Is my body weight this morning a couple pounds (or about 1%) lower than it was yesterday morning?  If you answer yes to any one of these questions, you might be dehydrated.  Answer yes to two and you are dehydrated and need to rethink your approach to fluids in your diet. 

Water affects every part of your body:

It keeps your throat, mouth and lips moist, helping to prevent bad breath and dental caries.

Dehydration lowers your blood volume, so your heart must work harder to pump the reduced amount of blood and get enough oxygen to your cells, which makes everyday activities like walking up stairs—as well as exercise—more difficult.

Your body releases heat by expanding blood vessels close to the skin’s surface (this is why your face gets red during exercise), resulting in more blood flow and more heat dissipated into the air.  When you’re dehydrated, it takes a higher environmental temperature to trigger blood vessels to widen, so you stay hotter.

When you’re well-hydrated, the water inside and outside the cells of contracting muscles provides adequate nutrients and removes waste.  Contrary to popular belief, muscle cramps do not appear to be related to dehydration, but instead to muscle fatigue. 

Staying hydrated keeps your memory sharp, your mood stable and your motivation intact.  When you’re well-hydrated, you can also think through a problem more easily. 

When a person is severely dehydrated, skin is less elastic.  This is different than dry skin, which is usually the result of soap, hot water and exposure to dry air. 

Your kidneys need water to filter waste from the blood and excrete it in the urine.  Keeping hydrated may also help prevent urinary tract infections and kidney stones.  If you’re severely dehydrated, your kidneys may stop working, causing toxins to build up in your body.

How much?

The Institute of Medicine says adult men need about 13 cups (3 liters) per day and adult women need about 9 cups (2.2 liters) per day.  But one size doesn’t fit all, so monitor your urine color: the lighter it is, the better hydrated you are.  In hot weather you need to drink more because you sweat more, especially if you’re exercising.  Humidity also increases your water needs.  When it’s humid and warm—a double whammy—you may need as much as two times more water than when it’s drier.    You also lose more water when breathing frigid, dry air. 

About 20% of fluid intake—or about 2.5 cups daily--comes from our food.  All foods contain some water, and fruits and vegetables deliver the most.  While caffeine is technically a diuretic (it increases water excretion from our bodies), you retain most of the water from caffeinated beverages.  Alcohol, on the other hand, particularly at high doses, can cause you to excrete more fluids than you consume. 

Sodium, potassium, chloride, calcium and magnesium are essential for vital reactions in your body—all are electrolytes and are lost in sweat.  It’s important that the concentration of these electrolytes doesn’t get too low or too high—and that they are replaced when depleted.  If your electrolyte balances are out of whack, you won’t properly absorb the water you drink.  Most electrolytes can be replenished with regular, healthy meals. 

Choosing water in place of calorie-containing beverages can lower overall calorie intake and help control weight.  Also, drinking water before a meal can help you eat less. 

Keep in mind that it is possible to overdo it.  You can drink too much water.  Water intoxication, or hyponatremia, is a serious condition when blood sodium levels precipitously drop.  This can be caused by profuse sweating and/or drinking too much water.  Hyponatremia could happen to someone who engages in a long athletic event, such as a marathon or multi-day hike.  Symptoms include confusion, disorientation, weakness and nausea.  Hyponatremia can lead to seizures, coma and death without prompt medical attention.

Be sure to pay attention to your fluid intake, especially in hot, humid weather.  And if you think you’re not drinking enough water, you’re probably right!

Source: Rachael Moeller Gorman