Importance of Water in the Human Body
Water Supports All Human Body Functions
The human body cannot survive without enough water; in fact, we can only last about 100 hours, give or take, without it. Water helps us moisten food (through our saliva), digest food (through our gastric secretions), transport oxygen and nutrients to and from our cells (via our blood), discard waste (through our urine and stools), and dissipate heat (through sweat and our breath). Water is the principal component of our muscles and organs. Water makes up about sixty (60) percent of an adult human male's total body weight until after age 50, and approximately fifty (50) percent of an adult human female's body weight. After age 50, this drops to about fifty-six (56) percent in males and forty-seven percent in females. The reason for the difference in water content between men and women has to do with the difference in fat levels, while the drop in the elderly has to do with their replacing muscle mass with fat. Once allowance is made for the fat content, there is very little difference between men and women, old or young, from childhood on.
Symptoms of Dehydration
The following are just a few symptoms of possible dehydration:
- Dry or sticky mouth
- Dry skin
- Swollen tongue
- Weakness, sleepiness, tiredness or exhaustion
- Decreased urine output
- Inability to sweat
- Muscle cramps
- Heart palpitations (a jumpy feeling, or a feeling that your heart is racing or pounding)
The color of your urine may also be an indicator of dehydration. Typically healthy urine is light in color and odorless. If your urine changes color to a deep yellow or yellow-orange, then you may be dehydrated.
Body Water Loss
Our bodies lose more water on a daily basis than any other essential nutrient. We lose water through our skin, by sweating when our body needs to shake off excess heat, but also by simple skin surface evaporation (a loss we do not really detect). We lose water when we pass urine. We lose water through our feces (stools). We even lose water when we breathe. Known as respiratory water loss, it is water that humidifies the air we breathe in (inhale) and that we then exhale as water vapor. Typically, a moderately active healthy adult at rest, with no stress, disease or illness, loses approximately 1,500 to 1,600 milliliters of water on a daily basis (or about 1.59 quarts per day). This water loss needs to be replenished on a daily basis in order to avoid dehydration.
Water and Fluid Intake
There are two ways we take fluids (water being chief among them) into our system: externally and internally. External intake means the fluids and foods we take into our bodies orally (or by IV, if we are in a coma or on a respirator or otherwise cannot feed ourselves). Internal intake is through our own metabolism's production of water.
Metabolic water is produced through the oxidation process of the food we consume. However, this process only gives us about eight (8) to ten (10) percent of our water requirement through metabolic water production.
Since the foods we eat were all once living organisms, food is an invaluable source of water for our bodies. The best source of water comes from fruits and vegetables with a high water content, as shown in the tables below.
High Water Content Fruits
Water Content Percentage
Dark Green Leafy Vegetables Help Satisfy Your Water Intake Needs
High Water Content Vegetables
Water Content Percentage
Recommended Daily Water Requirement
To restore water balance to your body and replace the fluids lost during normal day-to-day activities (and more during exercise), the recommended daily water or fluid intake is still the "eight-eight rule:" eight 8-ounce glasses of water a day. However, the exact amount needed really does vary by individual. Influencing factors include where you live (cold, temperate or tropical climate), how much you weigh, and how active you are. To get a slightly more accurate requirement you can use on-line calculators, such as Medindia's Daily Water Intake Calculator, or apps. Or else you can use the following formula, taken from myfooddiary.com: half an ounce of fluid intake per day, for every pound of body weight.
And don't worry about drinking too much; your kidneys will excrete any excess fluid, thereby regulating your body fluid levels.
Of course, if you have a chronic condition, such as diabetes, whereby your body retains too much fluid, or, conversely, has a hard time retaining the optimal or required level of fluids, you really must see your doctor to ensure achieving optimal water balance.