Why does common advice stipulate that you must consume pure water for hydration? Won’t things with any amount of water in them hydrate you, proportional to the water content?

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Why does common advice stipulate that you must consume pure water for hydration? Won’t things with any amount of water in them hydrate you, proportional to the water content?

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Yes. The reason people suggest water in particular is because juices and sodas have a LOT of sugar in them, and it’s the easiest way for a dieter to cut out excess calories. (A can of Coke has as many calories as a candy bar, and like the candy bar, it’s mostly sugar.)

Drinking 2 liters of beverage every day is enough to keep you hydrated. Just be careful if you’re watching your sugar or caffeine intake. 🙂

All water will hydrate you, but other things mixed in with the water may counteract that hydration.

For example, sea water is so salty that it will start to mess up your kidneys and thus pose a bigger threat over time. Coffee and alcohol are diuretic, basically meaning they make you pee more which will end up flushing some of that water right back out of your system. Things like soda and juices can have tons of sugar in them, meaning they’re not exactly healthy in excess and can lead to obesity or diabetes if consumed far too often.

Overall, pure water doesn’t really have negative side effects to consider, especially if hydration is the only thing you’re worried about.

>ELI5 Why does common advice stipulate that you must consume pure water for hydration? Won’t things with any amount of water in them hydrate you, proportional to the water content?

Not if the body needs to expend more water to separate that water content from the other ingredients. Salt water has approximately the exact same “water content” as fresh water or even distilled water – the differences are rounding errors. Yet it will not hydrate you since your body does not receive those resources in neat separated piles – here’s the H2O, here’s a pile of NaCL – but has to do all the processing itself. And your kidneys can only concentrate salts in your waste to a certain degree, not arbitrarily. So now the body has to *expend* water to dilute the salt water in order to get rid of it.

Hydration is interesting because you want to avoid both extremes on the spectrum of water purity. If the water you drink has too much stuff in it, like Soda, that’s bad and won’t hydrate you. But if the water you drink has absolutely nothing in it, like distilled water, that’s also bad and will sap your body of salts. This is why even purified water isn’t truly pure H2O and belongs in a different category as distilled water. And it is the same reason that drinks like Gatorade are considered to be more hydrating.

The issue with having too much stuff in the water is that water serves as a catalyst in the body. This means that water is used to make processes happen, and if you don’t have enough water, those processes don’t happen smoothly. These processes also include separating the things you ingest down into their basic parts. So if the only beverages that you consume have lots of stuff suspended in the water (coffee, soda, tea) then it takes a lot of water to break it down. In most cases, the water that it takes to break down these beverages is either equal to, or even more than, the amount of water that the beverage itself contributes to the body. So by drinking it, you are using up whatever hydration it provides just in order to process it. And in this way you don’t actually end up adding water to your body in any meaningful way.

For distilled water, the problem becomes that it is so pure. Water is a polarized molecule that easily bonds with ions. This means that due to how the oxygen and hydrogen atoms are arranged within the water molecule, it has a slight positive charge on one side. Ions are atoms or molecules that carry a slight negative charge that are used for certain processes within the body. For example, sodium and calcium ions are used to allow nerves to communicate with one another. If you ingest distilled water, this slight positive charge of the H2O molecules readily attracts the loose ions with their slight negative charge and saps your body of the ions that it needs to function. And since the water you are ingesting is not carrying in anything, it depletes your reserves. So while it provides H2O that doesn’t need to be used up to process what you drank, it still does more harm than good to drink distilled water.

These two reasons is why the most hydrating and healthy to drink water has something in it (to prevent the pure H2O from sapping your ions), but not too much stuff in it (so that you can actually store some of the water instead of using it all up right away). This brings us back to Gatorade. This is a drink specifically designed to be water plus electrolytes for hydration and replacing if salts that are sweated out. Electrolytes is a broad term for the elemental ions that our body needs to function. These include, but are not limited to, sodium, potassium, and magnesium. This means that it doesn’t carry lots of “unnecessary” stuff in it that would require over processing, but also that it carries in the ions that distilled water would strip out. The biggest thing to be careful of with drinks like Gatorade though, is the high sugar content that is added to make it more marketable. A concoction of the purely the ions that are good for you doesn’t taste that great, so they have to add extra stuff to make it appealing to the masses.

The conclusion of it all is that you should avoid “pure” water like distilled water altogether, and you should limit the amount of other types of beverages (coffee, soda, tea, fruit juice) that you drink. Then you should be supplementing your hydration by drinking regular water as the majority of your beverage intake. This water can be spring water, purified water, or tap water (filtered or unfiltered). These types of water still have stuff in them, like chlorine and fluorine in tap water, that prevent the H2O from stripping ions out of your body like distilled water would. But they are still pure enough that they provide adequate hydration by not carrying tons of stuff into your body that would require lots of processing.

Just remember that everything you put into your body requires water for your body to process it. You are also always losing water through urination. So you need to drink enough water to balance out whatever you consume and whatever water you lose. A good rule of thumb can be that for every meal, you should be drinking one tall glass of water. And for every non-water beverage you consume, you should be drinking an equal amount of water.

There was a study a while back that talked about how much water should be consumed daily for optimal health. The study specified that the water can come from any source. It even cited the water in a baked potato counting towards the daily total.

A bottled water company got hold of that study and just left out the bits that didn’t agree with their marketing strategy. So they talked about X glasses of water (and only water), naturally their water was the best for it.

That bit of marketing BS caught in the public psyche and now people think you have drink only water for hydration. Even though that is as big an old wives’ tale as not swimming for half an hour after you eat.