It's necessary for life to exist, makes you healthier, and it's incredibly refreshing especially after an intense workout.

水對生命的存在不可或缺，它能讓人更健康、精神抖擻，特別是在劇烈運動後。

But is water intoxication a real thing?

但水中毒是真的嗎？

Can you drink too much water?

真的有可能喝「太多」水嗎？

We're often told to drink around 8 glasses of water a day to stay healthy,

常常聽人說，一天要喝八杯水才健康。

but the honest truth is that this specific number is somewhat arbitrary, and no scientific research exists to support it.

但事實上這個傳言沒有事實根據，也沒有科學研究證實這個論點。

Regardless, we know water is incredibly important; in fact, every organism we know of requires water to survive.

儘管如此，水還是非常重要；事實上，任何生物都需要水才能存活。

Not only does it help the human body to bring oxygen and nutrients to the cells, regulate body temperatures and aid metabolism, but it flushes waste out of the body.

水不只幫助人體傳送氧氣及養分到細胞、平衡體溫、幫助代謝，還可以排泄掉人體的廢物。

Sweat out too much during a sporting event, and you'll start to feel a bit woozy.

如果運動時流太多汗，你會感到頭暈目眩。

Three days without water, and you likely won't survive.

而如果三天沒喝水，你可能就無法存活。

So how could such an essential substance hurt us? It all comes down to the cellular level.

那麼，人體這麼重要的必須元素又怎麼會傷害我們呢？這要從細胞層面說起。

The water you drink has very few electrolytes in it - things like sodium or potassium - especially compared to your cells.

比起身體的細胞，我們喝的水裡所含的像是鈉或鉀這類電解質其實非常少。

The electrolytes in your cells allow your muscles and nerves to work properly, and help to control blood pressure and blood volume.

細胞內的電解質能讓肌肉及神經順利運作，同時也幫助控制血壓及血液濃度。

Without them, your body cannot function.

少了電解質，身體就無法順利運作。

Now normally, the difference in the electrolyte concentration inside and outside the cell wouldn't pose a problem, because your kidneys flush out any excess water.

一般情況下，細胞內外的電解質濃度差不有什麼問題，因為腎臟會排除多餘的水份。

However, the kidneys can only excrete fluid at a certain rate.

然而，腎臟只能排泄一定比例的水分。

This means that consuming a lot of water in a short period of time creates a large concentration difference.

這就表示，短時間內攝取太多水份會造成很大的濃度差異。

As a result, water is drawn into the cells in an attempt to dilute the concentration and even out the proportion of electrolytes, and this causes the cells to swell.

如此一來，細胞就會吸收水份以平衡細胞內外電解質濃度，而這就造成了細胞膨脹。

The problem is, unlike other parts of your body, the brain literally has no room inside the skull for these newly plump cells.

問題在於，不同於身體其他部位，腦部並沒有多餘空間讓細胞膨脹。

This results in extreme headaches and confusion, leading to seizures, comas, respiratory arrest and even death.

也就造成了劇烈頭痛、頭暈、癲癇、昏迷、呼吸驟停等症狀，嚴重甚至可能死亡。

So should you be worried? Not likely!

那我們應該要擔心水中毒嗎？其實不用！

Cases of water intoxication are very rare, though they do happen in extreme circumstances.

水中毒的情況非常罕見，儘管它們確實會在極端狀況下發生。

Close to 1/6 of marathon runners develop mild cases in their careers, with all endurance athletes at a higher risk.

大約有 1/6 的馬拉松選手曾經發生過輕微水中毒症狀，所有耐力性項目選手都比常人有更高的水中毒風險。

This is because under the extremes of athletic stress, the body attempts to conserve water.

因為在這類運動的極限壓力下，身體會自動儲存水分。

So not only are you taking more water in, you're peeing less out.

所以從事這些運動時，你不只喝了更多水，小便的次數同時也減少。

Science says, though you're not likely to suffer from water intoxication, you should drink to your thirst - it's the best indicator!

根據科學，雖然你不太可能水中毒，但感到口渴時就該喝水，這是最直接的指標！

Don't forget: we have a new video out every day during the Olympics.

別忘了，在奧運期間，每天都會有新影片出爐喔！

But if you can't wait, head to cbc.ca/olympics/ScienceSays for more.

如果迫不及待，可以直接上 cbc.ca/olympics/ScienceSays 搜尋更多影片。

Keep asking those burning questions with the hashtag ScienceSays, and subscribe for more awesome science videos!

使用 #ScienceSays 提問，並訂閱查看更多優質科學影片！