According to the Mayo Clinic, every bodily system relies on water, so without enough, the body struggles to function. When it can’t fulfill its normal operations due to a water deficit, the condition is called dehydration. It only takes a water loss of three to five percent of a person’s body weight before mild dehydration occurs, causing an increased heart rate, difficulty concentrating, headache and dizziness. A more serious case of dehydration can cause shock, kidney failure and death.
Best to avoid it by getting enough liquid every day. And that’s the tricky part, for the daily amount of water each person needs varies. Indeed, it varies not only between individuals, but also according to a single individual’s changing circumstances. Sometimes water needs change from hour to hour. Factors like health, environment and activity level all adjust a person’s water needs.
Since needs do vary, a person should begin by taking in a baseline amount of water and then take a cue from the body’s reaction to hydration efforts. If urine is plentiful and clear or pale yellow, and there is little or no thirst, water needs are likely being fulfilled.
When they aren’t being filled, an individual experiences thirst. Urine turns darker as it becomes concentrated. Infrequent urination over a day’s time is also a symptom of mild dehydration. A person showing signs of dehydration when others don’t might have a larger water intake need. Remember — every person’s “right” amount of water can be different.
Conventional wisdom as a starting point
The so-called eight by eight rule is an easy-to-remember guideline for how much water a person needs to drink. It advises everyone to drink eight, 8-ounce glasses daily. This conventional wisdom can be used as a starting point, though it doesn’t take into consideration an individual’s situation, those factors that might increase water needs. Still, eight cups of water coupled with the other beverages drunk during a day, along with fluids obtained from eating, may, indeed, succeed in providing a person enough daily liquids to avoid dehydration.
As long as a person is alert to bodily signals for more water, using conventional wisdom as a starting point might work. Others may like things more exact. Learning who needs more or less water and why can fine tune an estimation for how much water an individual needs in a day.
Permanent and semi-permanent factors that influence water intake needs are
• Gender. A man needs more water than a woman.
• Age. An adult needs more water than a child.
• Typical activity level. A sedentary person needs less water than an active person.
• Health considerations. A pregnant woman needs more water, as does a woman who is breastfeeding. Chronic health conditions may affect how much water a person needs, so individuals should talk to their health care providers.
Fluctuating water needs
Some circumstantial factors can change the amount of water needed from day to day or even from hour to hour. Activity level is one such factor. During exercise, it’s important to replace water lost through perspiration. Drink water during workout routines.
A person may need less water during a day if drinking other liquids like juice. Food itself supplies about 20 percent of a person’s need for liquid, according to the Institute of Medicine. Foods like watermelon, celery, carrots and potatoes in particular contain a lot of water.
An illness such as a flu or a fever can temporarily increase the amount of water needed to maintain hydration. Additionally, medications can alter the amount of fluid a person retains or loses.
Environmental conditions can change the amount of water needed. For instance, dry, heated air in the winter allows more moisture to be lost from the skin, so increasing water intake is warranted. The weather itself can change water needs. A hot and humid day calls for more water, especially for those who must be active outside.
For those who’d like to more closely monitor water intake, the Institute of Medicine released guidelines in 2004. According to the institute, as a baseline men should have a total daily fluid intake about 125 ounces and women should take in 91 ounces. Pregnant or breastfeeding women should consume 10 and 13 cups of fluid respectively. Fluid intake is the total of water, other beverages and food.
Knowing that about 80 percent of fluid intake comes from water and beverages allows individuals to calculate a baseline for liquid consumption. A person shouldn’t get too worried about measuring exact amounts. Most people are able to keep themselves hydrated by simply drinking when thirsty, the institute says.