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  • Why does my bottled water have an expiration date? Does this stuff actually go bad?


  • Hi, everyone, Julian here for DNews.

    各位好,我是 DNews 的 Julian。

  • Have you ever left a glass of water out overnight, and the next day, taken a drink, and noticed it tasted funny?


  • Does that mean the water is going bad, or what's happening here?


  • Well, the water itself doesn't have any sugars or proteins like food, so microbes aren't consuming it and rotting it.


  • However, that's not to say the chemistry of the water hasn't changed.


  • By being exposed to air, the water absorbs some CO2, and a tiny portion of that, about 0.13%, is converted into carbonic acid.

    水暴露在空氣中時,會吸收一些二氧化碳,而其中的一小部分,大約 0.13%,會轉變為碳酸。

  • Some carbonic acid will then lose a proton or two, forming bicarbonate or carbonate respectively.


  • This lowers the pH of water, making it slightly acidic and changing the taste.


  • So, does that mean it's unsafe? Probably not, no, unless you are a shellfish.


  • Carbonic acid forms about 4 million times more bicarbonate than carbonate, and shellfish need carbonate to build their shells.


  • The bias towards bicarbonate production means they have less to build their shells from.


  • Not only that, but the higher acidity can actually dissolve shells.


  • Since the Industrial Revolution, the ocean surface has become slightly more acidic.


  • So, if you love oysters, there's another reason to care about CO2 in the atmosphere.


  • Anyway, if you're a human, the small shift in pH isn't going to be what hurts you.


  • The problem is water in an unsealed container has been exposed to bacteria.


  • 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.


  • Water left outside can also start growing algae and host mosquito larvae, which will make you sick and is gross to think about,


  • but not as gross as thinking about the dust inside your house landing in your water.


  • It can be purified with chemicals, like iodine or chlorine, or it can be filtered and boiled, and it'll be good as new.


  • Again, it's not the H2O breaking down and going bad, it's just hosting other nastiness that spoils the taste.


  • 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.


  • When they set out for long voyages, Europeans sailors had stores of water in wooden barrels.


  • After a few weeks though, it would start to grow algae. So to get around this, sailors also brought along beer.


  • And when that beer ran out, they switched to that old pirate favorite, rum.


  • The alcohol in the beer and rum killed off bacteria, but the side effect was drunken sailors early in the morning.


  • In fact, British sailors actually got a daily rum ration until 1970.

    實際上,英國水手截至 1970 年以前,每日都有蘭姆酒配給。

  • Now, though, we can store water indefinitely without having to worry about its safety, provided it's stored correctly.


  • The CDC says commercially bottled water is the safest, but it should still be stored out of direct sunlight.


  • Some plastics release a hormone disruptor called bisphenol-A, or BPA, into the water when heated.

    有些塑膠製品受熱時,會將賀爾蒙干擾素酚甲烷(簡稱 BPA)釋放到水中。

  • Plastic bottles are also permeable, so water should not be stored near pesticides or gasoline.


  • Aside from that, though, you don't have to worry about the expiration date on bottled water.


  • That's a holdover from old New Jersey law that has since been repealed because there's no scientific evidence to support it.


  • Gotta love it when science informs lawmaking!


  • So, now the question is, how much water do you actually need to drink?


  • Trace covers that here.

    Trace 在連結影片中會為各位說明。

  • A lot of our fluid intake comes from food. The rules say that we need to drink fluid.


  • So, if we eat a banana or an orange, we consume their fluid, which is to say, we take their water.


  • 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?


  • Let us know in the comments or on Facebook or Twitter.


  • Subscribe for more, and I'll see you next time on DNews.

    請訂閱以收看更多影片,我們下回 DNwes 再見。

Why does my bottled water have an expiration date? Does this stuff actually go bad?


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水會過期嗎? (Does Water Ever Expire?)

  • 94811 4351
    Jeng-Lan Lee 發佈於 2017 年 08 月 10 日