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Why does my bottled water have an expiration date? Does this stuff actually go bad?
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Hi, everyone, Julian here for DNews.
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Have you ever left a glass of water out overnight, and the next day, taken a drink, and noticed it tasted funny?
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Does that mean the water is going bad, or what's happening here?
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Well, the water itself doesn't have any sugars or proteins like food, so microbes aren't consuming it and rotting it.
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However, that's not to say the chemistry of the water hasn't changed.
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By being exposed to air, the water absorbs some CO2, and a tiny portion of that, about 0.13%, is converted into carbonic acid.
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Some carbonic acid will then lose a proton or two, forming bicarbonate or carbonate respectively.
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This lowers the pH of water, making it slightly acidic and changing the taste.
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So, does that mean it's unsafe? Probably not, no, unless you are a shellfish.
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Carbonic acid forms about 4 million times more bicarbonate than carbonate, and shellfish need carbonate to build their shells.
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The bias towards bicarbonate production means they have less to build their shells from.
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Not only that, but the higher acidity can actually dissolve shells.
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Since the Industrial Revolution, the ocean surface has become slightly more acidic.
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So, if you love oysters, there's another reason to care about CO2 in the atmosphere.
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Anyway, if you're a human, the small shift in pH isn't going to be what hurts you.
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The problem is water in an unsealed container has been exposed to bacteria.
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Most tap and bottled water has chlorine additives, which will keep the microbes from multiplying for a day or two, but after that they can go crazy.
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Water left outside can also start growing algae and host mosquito larvae, which will make you sick and is gross to think about,
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but not as gross as thinking about the dust inside your house landing in your water.
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It can be purified with chemicals, like iodine or chlorine, or it can be filtered and boiled, and it'll be good as new.
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Again, it's not the H2O breaking down and going bad, it's just hosting other nastiness that spoils the taste.
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Our ancestors didn't have the benefit of germ theory or chemical purification, so when their water became unsanitary, they had to come up with a different solution.
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When they set out for long voyages, Europeans sailors had stores of water in wooden barrels.
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After a few weeks though, it would start to grow algae. So to get around this, sailors also brought along beer.
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And when that beer ran out, they switched to that old pirate favorite, rum.
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The alcohol in the beer and rum killed off bacteria, but the side effect was drunken sailors early in the morning.
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In fact, British sailors actually got a daily rum ration until 1970.
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Now, though, we can store water indefinitely without having to worry about its safety, provided it's stored correctly.
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The CDC says commercially bottled water is the safest, but it should still be stored out of direct sunlight.
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Some plastics release a hormone disruptor called bisphenol-A, or BPA, into the water when heated.
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Plastic bottles are also permeable, so water should not be stored near pesticides or gasoline.
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Aside from that, though, you don't have to worry about the expiration date on bottled water.
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That's a holdover from old New Jersey law that has since been repealed because there's no scientific evidence to support it.
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Gotta love it when science informs lawmaking!
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So, now the question is, how much water do you actually need to drink?
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Trace covers that here.
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A lot of our fluid intake comes from food. The rules say that we need to drink fluid.
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So, if we eat a banana or an orange, we consume their fluid, which is to say, we take their water.
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Have you gotten sick from drinking water? Did you switch to rum? Or do you have any other questions that you want us to field?
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Let us know in the comments or on Facebook or Twitter.
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Subscribe for more, and I'll see you next time on DNews.