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?

你有沒有試過把一杯水放過夜，隔天喝一口時發現味道怪怪的？

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

這是不是代表這杯水壞了，還是發生了什麼狀況？

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

其實，水並不像食物般含有糖或蛋白質，所以微生物無法在其中孶生並使其腐壞。

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

但這並不代表水的化學性質沒有改變。

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.

部分碳酸會解離出一到兩個質子，分別形成重碳酸鹽或碳酸鹽。

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

這使得水的酸鹼值降低，讓它呈現弱酸性並且產生味道的改變。

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

那麼，這意味著水已經不安全囉？其實並不是，除非你是貝類生物。

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

碳酸形成重碳酸鹽的能力比碳酸鹽高出四百萬倍，而貝類需要碳酸鹽來生成牠們的殼。

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

而碳酸轉換成重碳酸鹽的傾向意味著貝類將會缺少形成貝殼的原料。

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

不僅如此，酸性提高還可能會溶解貝殼。

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

自從工業革命以來，海水表層酸度已經小幅度地提高。

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

所以說，如果你愛吃生蠔，你又有了關注大氣中二氧化碳含量的理由了。

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

言歸正傳，你身為人類，小幅度的酸鹼變化對你沒有大礙。

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

問題是，裝在未完全密封容器中的水暴露於細菌威脅之中。

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.

大部分自來水或瓶裝水都含有氯添加劑以抑制細菌孶生，不過抑菌效果只能持續一兩天，之後細菌量可能就會失控。

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

曝露在空氣中的水也可能會滋生水藻和孑孓，使你生病，而且光想就覺得噁心，

but none as gross as thinking about the dust inside your house landing in your water.

但這噁心程度遠不及想像懸浮在屋內的灰塵落在你的水中。

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

當然，我們可以用碘或氯等化學藥劑來淨水，也可以採用過濾和煮沸的方式，讓水再次純淨。

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

再強調一次，這並不是水本身被分解腐壞，而是水中含有讓味道變怪的髒東西。

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.

人類的祖先沒有病菌致病學和化學淨水的知識，所以當他們的水變得不衛生時，他們得想出其他的解決方法。

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

當歐洲的水手要展開長途航行時，他們將水儲藏在木桶中。

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

但幾週過後，藻類便會開始在水中生長。為了解決這個問題，水手們還會帶上啤酒。

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

當啤酒喝完時，他們改喝海盜的最愛：蘭姆酒。

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

啤酒和蘭姆酒中的酒精可以殺死細菌，但副作用是，一大清早就醉醺醺的水手。

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.

如今，我們可以無限期地儲水，而不用擔心水的飲用安全性，當然前提是，水的儲藏方法要對。

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

美國疾病管制與預防中心表示，市售瓶裝水是最安全的，但它必須被儲藏在不受陽光直射的地方。

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

有些塑膠製品在受熱時會將賀爾蒙干擾素——雙酚A（簡稱 BPA）釋放到水中。

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

同時，塑膠瓶具有滲透性，因此它們不應該被儲藏在靠近殺蟲劑和汽油的地方。

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

除了以上情形，你大可以不用擔心瓶裝水上的保存期限。

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

這只是紐澤西的一條舊法令罷了，它現在已經被廢止，因為沒有足夠的科學證據支持。

Gotta love it when science informs lawmaking!

當科學影響立法時，真是大快人心！

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

所以現在的問題是，你究竟需要喝多少水？

Trace covers that here.

Trace 在這支影片中進行了說明。

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

我們很多的液體攝取來源都是食物。我們被告知要多喝水。

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

所以當我們吃一根香蕉或是一顆橘子時，我們攝取了它們的液體，也就是說，我們搶了它們的水分。

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?

你是否曾經因為喝水而生病？你改喝蘭姆酒了嗎？還是你有其他想要我們回答的問題？

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

請在底下留言，或是透過 Facebook 或 Twitter 告訴我們。

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。