The human body, which is made up of between 55 and 75 percent water (lean people have more water in their bodies because muscle holds more water than fat), is in need of constant water replenishment. Your lungs expel between two and four cups of water each day through normal breathing – even more on a cold day. If your feet sweat, there goes another cup of water. If you make half a dozen trips to the bathroom during the day, that’s six cups of water. If you perspire, you expel about two cups of water (which doesn’t include exercise-induced perspiration).
Health benefits of water
Water is crucial to your health. It makes up, on average, 60 percent of your body weight. Every system in your body depends on water.
Lack of water can lead to dehydration, a condition that occurs when you don’t have enough water in your body to carry on normal functions. Even mild dehydration – as little as a 1 percent to 2 percent loss of your body weight – can sap your energy and make you tired. Dehydration poses a particular health risk for the very young and the very old. Signs and symptoms of dehydration include:
- Excessive thirst
- Dry mouth
- Little or no urination
- Muscle weakness
How much water do you need?
Every day you lose water through sweating – noticeable and unnoticeable – exhaling, urinating and bowel movements. For your body to function properly, you need to replace this water by consuming beverages and foods that contain water. So how much water, or more precisely fluid, do you need?
This isn’t an easy question to answer. A healthy adult’s daily fluid intake can vary widely. Most people drink fluid to quench thirst, to supply perceived water needs and “out of habit.” At least three approaches estimate total fluid (water) needs for healthy, sedentary adults living in a temperate climate.
The average urine output for adults is 1.5 litres a day. You lose close to an additional litre of water a day through breathing, sweating and bowel movements. Food usually accounts for 20 percent of your fluid intake, so you if you consume 2 litres of water or other beverages a day (a little more than 8 cups), along with your normal diet, you can replace the lost fluids.
Eight 8-ounce glasses of water a day
Another approach to water intake is the “8 x 8 rule” – drink eight 8-ounce glasses of water a day (about 1.9 litres). The rule could also be stated, “Drink eight 8-ounce glasses of fluid a day,” as all fluids count toward the daily total. Though this approach isn’t supported by scientific evidence, many people use this basic rule as a guideline for how much water and other fluids to drink.
The Institute of Medicine recommends that men consume 3 litres (about 13 cups) of total beverages a day and women consume 2.2 litres (about 9 cups) of total beverages a day. These guidelines are based on national food surveys that assessed people’s average fluid intakes.
You can choose any of these fluid intake approaches to gauge your fluid needs. But your current total fluid intake is probably OK if you drink enough water to quench your thirst, produce a colourless or slightly yellow normal amount of urine, and feel well.