How Much Water Should You Drink a Day?
The professor was blunt, asking: “Where’s the proof?”
That was the message of Dr. Heinz Vatlin, a highly respected Dartmouth professor writing in the American Journal of Physiology: Regulatory, Integrative and Comparative Physiology.
He’d taken aim at a seemingly unquestionable institution in health. Namely, the idea that you should drink eight glasses filled with at least 8 ounces of water per day, a.k.a. “8x8.”
His conclusion: The recommendation was completely unfounded. 
It turns out a lot of the conventional wisdom about hydration is either not based on science—or just plain wrong. But don’t sweat it. This article will separate myth from fact so you can hydrate properly and feel better every day.
Factors Affecting How Much Water You Should Drink Per Day
The amount of water you should drink per day depends on who you are and what you do. For example, the total can vary based on your body type, gender, age, health issues, metabolism, and even ongoing weight loss.
As a starting point, you can look to the National Academies of Sciences, which suggests:
- Women aim for about 90 ounces of total water each day
- Men take in around 125 ounces of total water in a given day
Note the term “total water,” which means it includes fluids from water-rich foods like fruits and vegetables. 
But again, those are averages, which need to be adjusted for you specifically. For example…
Professionals say you ought to aim to get one-half to one time your body weight in ounces of water. That means a 120-pound woman would want somewhere between 7.5 and up to 12 8-ounce glasses of water per day, while a 200-pound male ought to aim between 12.5 and 25 8-ounce glasses.
If that sounds like a lot of fluids, that’s because it is. And as we’re about to discuss, forcing down fluids is not a good idea (see “Can You Drink Too Much Water?”, below).
Women have higher levels of progesterone, a hormone which can cause the kidneys to excrete more sodium. For that reason, some—especially active women—may want to consider adding a little more salt to their diet during the days leading up to and during their period. 
As you age, your thirst levels become less of an acute indicator of hydration. Kidney function can deteriorate, leading to the need for increased urination. 
Taking certain medications increases your hydration needs, according to the National Institute on Aging.  (Learn more about how Mucinex and other common cold medicines affect your hydration status.)
A 2016 review in Frontiers in Nutrition found that increased hydration can be helpful to weight loss. Researchers credited two possible mechanisms: 1) decreased feeding (since people felt more full from taking in more water), and 2) increased lipolysis, meaning the body was better able to break down fat when sufficiently hydrated. 
What Are the Benefits of Drinking Water? (Besides Not Dying...)
Water is essential for the body. If you go too long without water, death is the outcome. And while most readers of this article will never be in a situation that severe, it’s also notable that there’s more to water than merely keeping you alive.
To understand how water can help the human body, let’s look at what happens as you become dehydrated.
Short-term dehydration, which happens when you don’t drink enough water for a few days, can result in:
- unclear thinking
- mood change
- feeling thirsty and having a dry mouth
- dry skin, eyes, and lips
- urinating less than usual  
By helping you avoid these issues, staying hydrated is clearly helpful to your physical and mental well-being. A more stable mood, clearer thinking, and better temperature regulation are all benefits. Additionally, staying hydrated can help with losing weight, constipation, kidney stones, and even the risk of certain cancers.   
However, if you go too far with your hydration, other problems can arise.
Can You Drink Too Much Water?
Drinking too much water is a real possibility—especially for select groups of people. In fact, some otherwise very healthy, athletic people have fallen victim to overdrinking.
The condition is known as exercise-associated hyponatremia (EAH), and at least 12 athletes have been killed by it.  In EAH, a person drinks so much fluid volume that their sodium levels drop into dangerous territory, which leads to brain swelling.
Mild symptoms of hyponatremia include dizziness, puffiness, and nausea. Were one to continue to drink excessively, more severe symptoms include confusion, seizures, coma, and—potentially—death.
EAH is the most common among athletes who run long distances. A study of Boston Marathon runners discovered that nearly one-sixth of participants drank so much during the race that they’d gained weight, which indicates overhydration. 
When to Drink Water (Does it Matter?)
Generally speaking, the best time to drink water is when you are thirsty. Research indicates thirst is a good indicator of your hydration levels overall.
However, there are a couple of times during the day when drinking water may be slightly more helpful to your body.
- When you first wake up in the morning. Your body loses water and electrolytes during sleep. Meanwhile, you won’t have consumed anything during the eight hours or so you’ve been in bed. So a morning dose of both can help you rebalance your system and get your hydration on the right track for the new day.
- Immediately following a workout. You sweat water and electrolytes out. It only makes sense to put them back in. (Did you know dehydration can actually lead to back pain? Here’s how.)
Proper hydration isn’t as complicated as some would lead you to think. Your water intake should primarily be driven by thirst. Years of evolution has created a system we can trust, right in our own body. When the total water content of your body goes down, you get thirsty. It’s that simple.
Overdoing it is bad. So is under doing it. That’s why experts recommend a simple rule of thumb: Keep water with you at all times and drink when thirsty. If you’re exercising, ill, or just arising from bed, a hydration multiplier like Hydrant may be a good idea. It also can be helpful if you’re the type of person who just finds flavorless water to be boring and hard to drink.
Guidelines are good, but counting cups per day isn’t as important as the feeling you have.