Most of us know we should be drinking water. After all, it accounts for 50–60% of an adult’s body composition. We lose water even when we’re at rest, through functions such as breathing and perspiration. Certain factors—from age to activity level—amp up our need for water even further. (More on those factors in a minute.)
When we don’t get enough water, we generally don’t feel good. Being under-hydrated by as little as 2% can bring on headaches, fatigue, and other forms of discomfort.
The question is: How much water do we really need to drink? Many of us were taught the “8 x 8” rule as children, which calls for eight 8-ounce glasses a day. Or, maybe you’ve heard that it’s best to “chain sip” water throughout the day, regardless of thirst or other variables. In reality, our water needs are far more nuanced: There’s no one-size-fits-all recommendation for how much water to drink, and the number of glasses you need is specific to you.
How to calculate your ideal daily water intake
Multiple factors affect a person’s fluid requirements. These include:
- Activity level. During physical exertion, the body loses water through sweat. The more you perspire, the more water you’ll need to make up for fluid losses.
- Diet. Not all water comes from the tap. Fruit and veggies are important sources, too—and how much of them you eat helps determine how much water you need to drink. For reference, food accounts for about 20% of water intake on average in North America.
- Pregnancy status. People who are pregnant need more water than those who aren't, to support fetal development. Interesting fact: The body composition of a newborn is about 75% water—higher than that of a mature adult.
- Medications. Drugs that treat particular conditions may increase the body’s urine output, an effect that can increase daily water needs.
- Age. With age, the body develops a reduced capacity to store and conserve water, which may also increase the need to consume H2O.
- Season and climate. Exposure to hot weather increases fluid losses from sweat, which means more water is needed to replenish lost stores.
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Conditions that cause sweating. All forms of perspiration—not just heat-included sweating—amp up the body’s fluid requirements. Menopausal hot flashes and conditions such as hyperhidrosis are common causes of excessive sweating.
To gain a baseline understanding of your personal water needs, pull out a calculator and plug your age and weight into this quick, three-step formula:
1. Divide your weight in pounds by 2.2.
2. Multiply the result by the number below that applies to your age range:
- If you’re younger than 30, multiply by 40.
- If you’re 30–55 years old, multiply by 35.
- If you’re older than 55, multiply by 30.
3. Divide your result by 28.3. The answer is the estimated amount of water you require each day, in ounces.
For example, for a 50-year-old person who weighs 180 pounds:
- 180 divided by 2.2 = 81.8
- 81.8 multiplied by 35 = 2,863
- 2,863 divided by 28.3 = 101.1 ounces per day (about 3 litres)
It’s important to remember that this calculation will not produce an exact measure of your water needs, and that it reflects your approximate baseline water requirement from all sources, including food.
How to know if you’re drinking enough water
No formula needed for this one: To check if you’re hydrated, take a quick look at your urine. If it’s pale yellow, you’re probably drinking enough water. On the other hand, a dark yellow colour could be a sign that you need to amp up your hydration. Just bear in mind that urine colour isn’t a perfect indicator. A darker colour can also result from certain health conditions, medications, vitamin B2 supplements, and natural pigments in certain foods.
Know the other signs of dehydration
That’s why it’s helpful to be on the lookout for other signs that your water intake might be too low. Dehydration can also be marked by:
- Thirst
- Headache
- Dry mouth
- Difficulty concentrating
- Fatigue
Dehydration is associated with kidney stones. Otherwise, there’s little evidence linking dehydration with chronic disease. Occasional bouts of mild dehydration are common.
Thirst isn’t always first
Dehydration can kick in before you feel parched. By the time you notice a dry mouth, your mood or concentration may already be affected by having too little water in the body. Keeping a refillable water bottle handy can be a visual reminder to sip regularly, before headaches and other forms of discomfort hit.
How can you increase your water intake?
If you’re thinking, “There’s no way I can chug so much plain water every day,” you have additional options for staying hydrated:
- Flavoured and bubbly water. If you like fizz in your glass, consider trying seltzer, sparkling water, or club soda—they hydrate just as well as still water. Or, give still water a flavour infusion by adding fresh fruit and herbs. Commercially bottled water containing non-nutritive sweeteners is another option if you want the flavour and convenience of a soft drink without the extra calories.
- Water-dense vegetables. Eating foods higher in water content can help keep you adequately hydrated, as well. Water-rich veggies include celery, bell peppers, zucchini, lettuce, and tomatoes. Try crunching on veggie sticks with salsa, or add an extra handful of chopped tomato to your salad.
- Water-dense fruits. Did you know that one orange contains up to 4 ounces of H2O? Along with citrus, water-dense fruits include melons, berries, and stone fruits (such as peaches).
Can drinking water help you lose weight?
Research has not established a direct link between water intake and weight loss. Water can support weight loss, however, when it takes the place of sugar-sweetened soft drinks. Unlike a can of sugary cola, water delivers hydration without adding calories to a person’s overall diet.
Other health benefits of drinking water
Good hydration is essential for:
- Regulating body temperature
- Supporting digestion
- Carrying nutrients and oxygen to cells
- Eliminating toxins via the kidneys
- Optimizing brain function
In a nutshell, water helps the entire body function at its best.
The upshot: Are you drinking enough water daily?
To boil it down, staying hydrated is important for your overall wellness journey. Because the body loses water throughout the day, replenishment is crucial for preventing dehydration. Your age and weight are key factors in how much fluid you need, with variables such as activity level and diet further influencing day-to-day water needs. Speak with a medical professional if you have any concerns about hydration and your health—especially if you notice unexplained changes in your level of thirst or in your urinary habits.