Staying Hydrated » The Unclouded Path

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How much liquid you should drink to stay hydrated is something of a public obsession. Fancy water bottles are like fashion accessories these days, and chances are you have one, too. You’ve also probably heard of the general rule of eight 8 oz glasses of water a day (the “8 x 8 rule”). But is it really something you need to follow? Do you really need to drink almost the equivalent of a 2-liter bottle of water every day to stay hydrated?

Origin of the 8 x 8 Rule

The rule says that for the average person in a temperate climate, you should drink at least eight 8 oz glasses of water (about 1.89 L) every day, excluding caffeinated and alcoholic drinks. This is in addition to the water that you get from food.

But, as with most info thrown around the Internet, it’s not backed by solid, scientific evidence. In fact, it’s not even clear where this tip came from. Heinz Valtin from Dartmouth Medical School did an extensive analysis on the subject, and the best he could come up with was a small passage at the end of a book by nutritionist Fredrick J. Stare. That passage said that the daily amount for an average adult should be about 6-8 glasses, including all beverages, and that fruits and vegetables are also good sources of water. The context of the passage also indicates that it’s more of a casual throwaway line than an evidence-backed suggestion.

Another possible origin of the 8 x 8 rule is a 1945 (yes it’s that old) guideline from the Food and Nutrition Board that says the daily intake should be about 2.5 L (or 1 mL for every calorie consumed) and that most of it would probably come from food. But it seems people left out the second part when coming up with the current rule.

Dehydration and Thirst

Before discussing how much water you actually need, it’s important to know what dehydration means and how your body avoids it. One of the two ways your body regulates the amount of water it needs is by monitoring blood volume. Certain cells in your kidneys secrete an enzyme called renin when it’s too low, and it sets off a series of reactions that tell your brain that you need both water and salt.

The other is by monitoring the concentration of solutes that are relevant to osmosis (like salt) in blood plasma. This is called osmotic concentration and is measured as a ratio between moles of the solute (osmoles, abbreviated Osm) and water. When the osmotic concentration gets too high, your brain gives you a signal in the form of thirst.

You may have heard that by the time you feel thirsty, you’re already dehydrated. Well, that’s not exactly correct. Dehydration sets in when your blood plasma’s at about 300 mOsm/kg of water (mOsm means milliosmole) or more, while impending dehydration (some call this mild dehydration) sets in at about 295 mOsm/kg of water. Thirst however, sets in at about 294 mOsm/kg of water. So you’ll be thirsty well before actual dehydration. The mechanisms behind thirst are very fine-tuned from millions of years of evolution, so it’s kind of hard to believe that a vital function like thirst would activate only when dehydration has already set in.

The exceptions to this are young kids (under 9 years old) and the elderly. Kids lose water faster than adults do, and they may not recognize the importance of thirst or be able to articulate their thirst well. Elderly people, on the other hand, have a reduced perception of thirst and can’t hold as much water in their bodies as younger adults.

How Much Water Should You Drink?

Well the short answer is it depends on the situation. For normal adults in a temperate climate doing mild physical activity, the Food and Nutrition Board recommends a total water intake (water from all beverages and food) of 3.7 L (125 oz) for men and 2.7 L (95 oz) for women. But for the vast majority of people, their daily intake is adequate just from relying on their sense of thirst. So, in a sense, most people should just follow Sprite’s slogan, “Obey Your Thirst”.

For people living in hotter/drier climates and/or doing strenuous activity, their needs are likely much higher. Hot weather and exercise make you lose more water through perspiration, and very dry weather will literally suck moisture out of your skin. As an example, someone working in very hot weather might need 4-6 glasses AN HOUR to stay hydrated.

Your health status affects your fluid needs, too. For example, pregnant or breastfeeding women need to increase their fluid intake. People with certain health problems, like urinary tract infections or kidney stones, need to increase the amount they drink, too.

Lastly, it’s important to note that how much water you drink at once affects how well your body retains it. For example, water that’s consumed over the course of 15 minutes is mostly dumped, while water that’s consumed over the course of 2.5 hours is mostly kept.

What Should You Drink?

It may come as a surprise, but just about any water-containing beverage will help you stay hydrated. A British study in Dec 2015 investigated the body’s ability to retain different fluids (what they called a fluid’s “hydration index”) and found that caffeinated and alcoholic drinks as well as sugary drinks had the same hydration index as water. In other words, the diuretic effects of caffeine and alcohol aren’t strong enough to make you dehydrated. Drinks with electrolytes (sodium and potassium) or complex nutrients, like Pedialyte and milk respectively, had the highest hydration indexes. This is because they take more time to process and therefore stay in your body longer.

Even so, water is probably the best beverage to ward off dehydration because it’s zero calories, readily available, and in some cases, free. It doesn’t have electrolytes, but you only start needing electrolyte-containing drinks after significant physical activity (more than an hour of intense exercise).

You can also get a large amount of water from eating certain foods like fruits, vegetables, and soups. Some foods, like watermelons, are almost entirely water.

Dangers of Drinking Too Little or Too Much Water

Too little water in your body leads to dehydration. On the other hand, too much leads to water intoxication. Both are potentially fatal.

Dehydration

Dehydration can happen in other ways other than drinking too little water. As mentioned before, environmental conditions and physical activity can play a role. Certain health problems, like severe vomiting or diarrhea, can also cause significant water loss. Here are some symptoms of dehydration:

dark urine (though dark urine doesn’t always mean dehydration)
low urine output
physical weakness
low blood pressure
dizziness
confusion
fatigue
seizures

Water Intoxication

Yes, it’s possible to overdose on water. Normally, your kidneys can handle a huge amount of water, so it’s rare to take in too much. But when you take in too much water in special cases like endurance sports or having reduced kidney function, or if you just drink an absurd amount of water, it can happen. Some dangerous drugs like MDMA (ecstasy) are especially bad in this respect. MDMA causes dehydration (which makes the body try to retain water) but also causes intense thirst, leading to over-drinking. The combination lowers the osmotic concentration of blood plasma quickly and can lead to death. These are some symptoms of water intoxication:

headache
confusion
drowsiness
muscle weakness/pain/twitching
high pulse pressure
sensory problems
nausea/vomiting

Some General Tips For Staying Hydrated

Here are some additional things you can do to make sure you get enough water:

Check the weather before you go out. If it’s going to be hot, and you’re going to be out for a while, bring water or some kind of drink with you.
Remember to get enough fluids at meals. You could also bring a few high-water snacks with you, like fruits or applesauce.
If you’re going on a long car trip, drink something that has a high hydration index, like milk. You could also just bring a regular drink with you, but you might need to look for bathroom stops more often.
If you’re going to be doing serious exercise, “pre-hydrate” before you do. That way your body has enough water when you start.
Be mindful of sun exposure. It can increase the rate you lose water.
Drink small amounts over time instead of all at once. As mentioned before, it will help you retain the water.
High elevation can mess with your perception of thirst. Be sure to drink a bit more if you’re doing physical activity at high altitudes, like hiking.
Remember to replace electrolytes if you’re sweating a lot. Drink a sports drink or take a some other electrolyte supplement during intense exercise.

Yue’s Recommendation

Bottled water can get expensive, so it’s best that you have a water filtration system at home. That way, you can have fresh drinking water at any time. But if you don’t have access to one, a Brita pitcher is the next best thing. In most places in the US, tap water is drinkable, but you may not like the taste due to the processes it’s been through to purify it. That’s where the Brita pitcher comes in. From my personal experience, the Brita pitcher removes most, if not all, of the other tastes associated with tap water.

There were a few minor problems that I had with mine though, but they were easily solved. The first was the somewhat flimsy lid on the reservoir. I just took off the lid entirely (instead of letting it flip open) when putting water into the reservoir. The second was that during the first use, a few bits of carbon dust from the filter showed up in the water. I just used it to water plants as the instructions suggested. The last one was that the colored top part wasn’t attached to the clear pitcher, so I needed to hold it with my thumb while I poured.

Except for those minor gripes, it’s great. I just put water into the reservoir and put the pitcher in the fridge. Pretty simple. Just remember to clean it after every use, and you’re set.