How Much Water Is Needed to Stay Hydrated?
Earlier this year, our readers took a poll – How much water do you drink per day? Most drink at least six cups of water per day, but 29 percent of our readers drink between three and six cups of water per day. And seven percent prefer to drink soda, coffee and/or juice instead of water.
So why do our bodies need water, and how much water should we drink per day? Dr. Stanley Goldfarb, a professor at PennMedicine, explains.
Why is it important to drink water?
Dr. Goldfarb: "We have a need for water intake every day, mostly because we have natural water losses from our body. Water loss occurs two ways – from our urine and from our skin. Generally, we need about 1 milliliter of water for every calorie consumed. That’s why most people take in about 2,500 milliliters (about 10.5 cups) of water per day, either by food or drink, in order to maintain a balance. Water that is lost from skin, whether you sweat or not, is lost through evaporation. Those two sources of water loss require us to take water in, and we know how much water to take in because of our natural thirst mechanism."
Why do our bodies need hydration?
Dr. Goldfarb: "Our bodies are made up of 60 to 80 percent water. Unfortunately, we’re kind of like a grape. When you squeeze a grape, you get rid of all the water, and it becomes a little raisin. Our bodies are like that. Our bodies require water in order for various chemicals and proteins to function optimally. Each cell in our body needs a certain level of water to function optimally. If we take in extra water, we need to get rid of it, because extra water doesn’t do the cell any good. On the other hand, if the cell loses water, then the cells also don’t function well. We need to maintain the proper amount of water in our bodies for cells to function."
What should we drink to stay hydrated? Water?
Dr. Goldfarb: "You don’t necessarily have to drink water. If you drink a soda, for example, that is made up of about 95 percent water. It’s still a liquid – basically water in some way. You don’t have to restrict yourself to plain water – any fluids will accomplish the same thing.
"Tap water is probably the safest form of water to drink because it’s tested, several times a day, by municipalities in the United States. Now, obviously, if you’re in a country that doesn’t have a good water system, that’s different, but in the United States, drinking tap water is very safe. Drinking bottled water is safe, as well - it’s just water. But bottled water is very expensive and produces a lot of waste. Also, there’s no evidence that drinking water from different parts of the world has any benefits.
"If you like to drink soda, and can put up with the sugar in it, or like the taste of sugar-free soda, or coffee, or tea – all of those things will provide adequate amounts of fluid, if that’s what you prefer to drink. I should point out that if you have problems with being overweight, it is better to drink water than sweetened beverages that can lead to excess caloric consumption.”
What about sports drinks?
Dr. Goldfarb: “It depends on the circumstances. The sports drinks are mostly water, and typically have a nice taste because of the added sugar. They do contain electrolytes, which are basically minerals, but it’s a pretty small amount of electrolytes, and most of the substances in these sports drinks tend to be sugar. For those who are exercising at peak physical exertion in a very hot and dry climate, they may benefit from a sports drink that helps replenish lost vitamins and minerals. But for someone working out in an air-conditioned gym for 30 minutes, it’s probably not necessary to consume sports drinks with electrolytes. It comes down to the strain put on the body and whether you need a sports drink or not. They are beneficial under extreme conditions. But, for the average person, under average physical strain, most sports drinks are unnecessary.
What happens if we don’t drink enough water each day?
Dr. Goldfarb: “Well, first of all, you’ll get thirsty. If we continue to lose water, particularly through our skin and through our kidneys, we could become dehydrated. Severe dehydration can be very dangerous. This can occur when an individual is in a very hot environment, sweating as much as a quart or more an hour. Some signs of severe dehydration are low blood pressure, changes in neurologic function, the skin becoming very dry, and intense sensations of thirst. But that’s a very extreme situation. On the other hand, if someone goes 3-4 hours without drinking any fluids, they can show signs of being thirsty. At that point, they’ve lost less than one percent of their total body water. They’ll feel a slight sense of dryness in their mouth and a sense of thirst. That doesn’t mean that they’ve reached a level of dehydration, it’s just a point where they need to drink some water. But, if they let it go to a severe state, it could become a severe problem.”
Can you drink too much water?
Dr. Goldfarb: “Yes, and people have actually harmed themselves doing so. There’s a notorious example from a radio show a few years ago. The radio show held a contest to see who could drink the most water over the shortest period of time. A lady drank so much water that she had a seizure and died. She overwhelmed her body’s ability to excrete water. It’s not easy to drink too much water. Really, our bodies are designed to get rid of water, and if people are just sipping water throughout the day, they won’t harm themselves. You would have to drink a very large amount of water, very quickly, to harm yourself.”
Can drinking water aid in weight loss?
Dr. Goldfarb: “There’s just no evidence to that, and actually, there’s pretty good evidence against it. The test comes from experiments of people who have been given water right before a meal and then, it’s observed how many calories are consumed afterwards. If you drink water right before a meal, or after a meal, you’re going to consume the same amount of calories; you’re not going to be filled up more quickly. However, if you flavor the water, for example, with a soup flavor, individuals tend to eat less during the meal. That doesn’t mean they eat less over a 24-hour period, because what likely happens is that they didn’t eat as much during the meal, making them hungry later. This idea of drinking water as part of a diet program really hasn’t been shown to be effective in a controlled study.”
Do we really need eight glasses of water a day?
Dr. Goldfarb: “You can drink what you like. The issue has become more about people forcing themselves to drink water that they really don’t want to drink. People who don’t want to drink water have been told that drinking a lot of water is going to have health benefits. That is not necessarily true.
“For the most part, our diets are balanced, and we take in a normal amount of food and are drinking a normal amount of fluids because we’re thirsty. That comes to about 2 ½ quarts or 3 quarts per day. That’s the average that people consume, and they excrete about 1 ½ quarts of urine per day. More fluid goes in than comes out because we have to remember the amount that is lost to our skin. By the end of the day, whatever fluid that is taken in, is taken out, and you stay in balance.
"On a normal basis, we take in about eight glasses of water per day, and people are sometimes confused that they need to drink eight glasses above and beyond what they’re already taking in. Based on your natural response to thirst, eight glasses a day is a normal amount to take in. But there’s no evidence that you need to force yourself to drink water. The National Academy of Sciences says to “drink when you’re thirsty.” That’s the best way to approach this issue. Unless you have a medical condition where a physician has recommended that you drink more fluid, it’s perfectly healthy to drink when you’re thirsty. The only time you should change that is if you’re going to be in a hot environment for a long period of time.”
Poll Question: Water – How much do you drink per day?