How Much Water Should I Drink Daily?
How much water should I be drinking? Not even our vast knowledge of the human body helps us out here — we mapped the human genome but we still don’t know exactly how much water a person “should” drink every day. Different studies release different numbers, and some doctors now think that each person’s essential water needs are different. So how much water should we be drinking? Let’s look at a few different takes.
What Does Water Do For Us?
So you know you need water but you don’t know why. Remember that water in some form makes up about 60 percent of your body weight. That means water is literally the most plentiful thing in your body. Each and every organ system in your body requires water to function. Water in your cells does a hundred different jobs at once — it can flush out toxins from your liver, provide the moist environment needed in your ear tissues, and brings nutrients back and forth between the cells. Water is the most important part of your body.
That’s why it is important to take in enough water. A lack of water will quickly lead to dehydration and eventually death. Dehydration occurs more often than people think — according to a recent study at Cornell, every time you feel thirst what you are feeling is the beginnings of dehydration. Without water, a human won’t survive more than a couple of days, though we can go without food for as long as a few weeks. When your body doesn’t have the water it needs to function, your first symptom is thirst, then a lack of energy and an overall feeling of tiredness. These symptoms worsen hour by hour until eventually the organ systems can’t function and shut down.
How Do We Lose Water?
People “lose” water in different ways, from urinating to breathing. That’s right, even breathing causes you to dehydrate a little. That’s why people who talk a lot at work (teachers, telemarketers, or people making business presentations) often have to “over hydrate”. Every day you lose water in sweat, bowel movements, and countless other functions. That’s why your body’s water supply has to be bolstered throughout the day. (See How to Lose Water Weight for more information.)
Drinking pure water isn’t the only way you rehydrate your body — any food or drink that contains water will hydrate your body. Water in juices, teas, and even sodas and coffee acts as a hydration agent, though ingredients in those foods are often dehydrators, so the total effect is neutral. Still, you don’t have to down gallons of water a day to replenish your water supply.
What Is the Replacement Method?
One of the most popular theories on the amount of water we should be drinking is called the “Replacement Method” or “Replacement Approach.” This method says that the human body should take in the amount that it puts out in urine. Since we just talked about the fact that urine is not the only way water leaves the body, you know this method is suspect. Still — many people live and die by the Replacement Method and it seems to work.
To figure out how much water you need to take in with the Replacement Approach, just consider your age. If you’re 16 or older, the Replacement Method says you should be drinking two liters of water a day — that is a little more than eight cups. That number is based on the estimated amount of fluid loss through urine. For people under the age of 16, the number is one and a half liters, though people are quick to point out that young children have different water needs entirely.
According to the Mayo Clinic, the average urine output for adults is about 1.5 liters (a little over 6 cups) a day. We lose about one liter (4 cups give or take) of water a day through breathing, sweating and bowel movements. Since you eat about 1/5th of your water intake in your diet, consuming about two liters of water or other beverages a day is plenty to replace your lost fluids.
Though the science behind the Replacement Approach is not perfect, their recommendation seems to check out when compared to other water intake theories.
What About “Eight Glasses a Day?”
It is especially interesting that the Replacement Method suggests a little over eight cups of water a day because the most common theory about water intake suggests eight cups as well.
We’ve all heard it — doctors repeat it over and over and most people seem to think it is the Gospel truth — “Eight 8-ounce glasses of water a day.”
Sometimes called the 8 by 8 rule (eight glasses with at least eight ounces of water a day) , you may as well just make sure you drink eight glasses of liquid a day. Though it is counter intuitive, all fluid intake works to rehydrate your body, even sodas and sugary drinks.
The 8 by 8 rule isn’t based on any real science, but it seems to be plenty of water for most people to keep their body hydrated, and based on the funny math we saw in the Replacement Method, it seems like enough liquid to replace what we lose in a day.
What Is the Gender Method?
There’s a third theory of water intake that recommends a different amount of water for males and females. This method is supported by the Institute of Medicine, and suggests that men should consume thirteen cups of liquid a day, while women can keep it to about nine glasses a day.
This is surprising because it is a higher amount of water than usually recommended by doctors or conventional wisdom. The things is — you almost can’t drink too much water. If you choose to drink ten glasses of liquid a day, good for you. If you want to just drink eight, you’re probably doing fine. The key is to replace the liquids you lose and to listen to what your body is telling you.
If you aren’t getting enough water, you’ll know. Stick to about eight glasses of liquid a day and stop worrying about drinking enough water.
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