The stock answer to the question "How much water to drink each day?" is: eight 8-ounce glasses. The real answer isn't that cut-and-dried.

© Russiangal | Dreamstime

“Drink eight 8-ounce glasses of water every day.” You’ve likely been hearing that mantra forever, and it’s worthy advice for staying hydrated. But is “eight glasses per day” a science-based recommendation—or one of those old axioms repeated so often that it’s become known as fact? The truth is, there are multiple considerations that come into play when considering how much water to drink every day.

Your health and locale, for example, can affect how much water you should drink. So too can your level of activity.

Below, we take a closer look at these and other intangibles. But let’s start with the question of what happens if we’re not drinking enough water. (See also our post “Do You Have Chronic Dehydration?“)

Dehydration Symptoms

The tried and true advice when it comes to how much water to drink is: “Listen to your body.” Here are 12 common symptoms of dehydration that should tip you off:

The question of how much water to drink hinges on such factors as your activity level, location, age, and health or health issues. [Photo: © Piotr Marcinski | Dreamstime]

1. Dry mouth
2. Dry eyes and/or blurry vision. (Note: Any part of the body that normally is moist can become dry and irritated when dehydrated, and eyes are no exception.)
3. Fatigue
4. Mood changes involving anger
5. Mood changes involving confusion
6. Muscle cramps
7. Headaches
8. Lack of sweat
9. Darker-colored urine
10. Dry skin
11. Skin that’s lacking in elasticity
12. And, in severe cases, a shrinking brain.

Conversely, staying well-hydrated—particularly via water, as opposed to other types of liquids (more on that in a minute)—translates into all kinds of health benefits. Water helps your body to maintain a normal temperature, aids in the process of flushing wastes, helps you maintain your energy level, and improves your complexion. It also boosts your immune system, prevents kidney stones, and helps you avoid constipation as well as headaches and cramps.

So… How Much Water to Drink?

But consider the symptoms you may experience when you’re dehydrated: dry mouth, dry eyes, headaches, cramps, fatigue, mood changes, and more. [Photo: © Piotr Marcinski | Dreamstime]

Your goal should be to avoid getting to the point of dehydration, but understandably, it happens—when we’re exercising hard, for example, or working in the yard, or spending a hot summer day at the beach. Fortunately, the situation is easily remedied by simply drinking water. If you meet what the National Academies of Science, Engineering, and Medicine calls your “daily hydration needs,” you shouldn’t get to that point.

The National Academy of Science recommends the following quantities for daily consumption. While they exceed the “eight 8-ounce glasses” advice, keep in mind that these amounts include not just water, but all manner of fluids—some healthy, some not so much:

• Around 11½ cups (93 ounces, or 2.7 liters) of fluids per day for women
• Around 15½ cups (125 ounces, or 3.7 liters) of fluids per day for men

So, drinking eight 8-ounce glasses (64 fluid ounces) is a worthy complement to other sources, including such beverages as coffee and tea and such foods as fruits (think watermelon), vegetables (spinach), soups, and stews. Typically, we get around 20 percent of our daily fluid intake from foods we eat.

Because our bodies differ, some of us need more fluids than others. The “right” amount can depend on such factors as:

• Your activity. If you’re engaged in an activity that makes you sweat, whether it’s gardening, playing a strenuous game of tennis, or hiking on a summer day, make sure you’re replacing your lost fluids with extra hydration.
• Your environment. The dog days of August, not to mention other summer months, typically require more fluids. High altitudes also can produce dehydration.
• Your health. Fighting a fever? Dealing with diarrhea? Then you’d need to adjust your water and fluid intake upward.
• Your age. Elderly people tend to take in less water and fluids than younger adults, a situation that can result in daytime fatigue. As we age, our need for water and our thirst for water can shift, resulting in lesser water intake and increasing the risk of dehydration. A widely publicized study in Australia during a 2003 heat wave showed that older adults tend not to drink adequate amounts of water. Their brains and bodies, according to findings published in Proceedings of the National Academy of Sciences, don’t coordinate sensory signals about thirst, so they become dehydrated during heat waves. (Elderly people who don’t drink enough water, according to ecaring.com, are “more susceptible to urinary tract infections, pneumonia, pressure ulcers, and confusion.”)

Are We Getting Enough Water?

We know it can be harmful to our bodies to become dehydrated, but do most people take heed? Actually, adults in the U.S. do, for the most part, according to a government report issued in 2015. The report’s data, which came from the U.S. National Health and Nutrition Examination Survey (conducted between 2009 and 2012 by the Centers for Disease Control and Prevention), showed that adult women exceed the daily recommended intake. Female participants of the study were drinking 93 ounces of fluid per day, or around 12 cups daily. Men were very close to their recommended 125 ounces, drinking some 117 ounces daily.

Of course, only 34 percent of the daily fluid intake by women in the study came from plain water; for men, around 30 percent of daily fluids came from water. The rest was coming via other sources, including healthy beverages like green tea but also sodas, sports drinks, and juices, which can be high in sugar and can lead to unwanted weight gain. Better to stick with water, the most effective hydrating liquid there is. (See our post “Weight-Loss Tip: Avoid Unnecessary Calories in Beverages.”)

Do our teens and children drink enough water? One study tells us that more than 50 percent aren’t ‘t well-hydrated, and it could result in physical and emotional health problems. [Photo: © Atikinka | Dreamstime]

Young People May Be Teetering on Dehydration

Younger generations, when it comes to the question of how much water to drink, are going in the wrong direction. The same study cited above assessed the drinking habits of more than 4,000 young people aged 6 to 19 years old. Researchers measured how concentrated each subject’s urine was (urine osmolality) in assessing whether participants were well-hydrated.

They discovered that more than 50 percent of all children and adolescents in the U.S. are not getting enough hydration. The trend, researchers say, could have an impact on the physical health and cognitive and emotional functioning of young people.

“These findings are significant because they highlight a potential health issue that has not been given a whole lot of attention in the past,” said the study’s lead author, Erica Kenney, a postdoctoral research fellow in the Department of Social and Behavoral Sciences at Harvard’s Chen School.

Kenney added that even though the hydration study results don’t reflect an “immediate, dramatic health threat,” the trend nevertheless could reduce the “quality of life and well-being for many, many children and youth.”