Water is virtually everywhere, from soil moisture and ice caps, to the cells inside our own bodies.
水几乎无所不在，从土壤水分及冰帽，到人体内的细胞。
Depending on factors like location, fat index, age, and sex, the average human is between 55-60% water.
依据一些因素，例如所在位置、脂肪、指数、年龄及性别而不同，一般人体内约有 55-60%是水分。
At birth, human babies are even wetter. Being 75% water, they are swimmingly similar to fish.
刚出生的婴儿甚至更多。水分占了全身的75%，和鱼的水含量很像。
But their water composition drops to 65% by their first birthday.
然而在周岁前，体内的水分会降至65%。
So what role does water play in our bodies, and how much do we actually need to drink to stay healthy?
那么，水在我们体内扮演什么角色呢？我们该喝多少水来维持健康呢？
The H20 in our bodies works to cushion and lubricate joints, regulate temperature,
水在人体内负责缓冲及润滑关节、调节体温、
and to nourish the brain and spinal cord. Water isn't only in our blood.
滋养大脑及脊髓。水不只是存在于血液中，
An adult's brain and heart are almost three quarters water.
成人的脑及心脏几乎 3/4 是水。
That's roughly equivalent to the amount of moisture in a banana.
大约等同於于1根香蕉的含水量。
Lungs are more similar to an apple at 83%.
肺比较类似苹果，有83%的水。
And even seemingly dry human bones are 31% water.
甚至看起来干燥的骨头都含有31%的水。
If we are essentially made of water, and surrounded by water, why do we still need to drink so much?
若我们主要是由水构成，并且生活周遭都有水，为何我们还需要喝那么多水？
Well, each day we lose two to three liters through our sweat, urine, and bowel movements, and even just from breathing.
我们每天流失2至3公升的水，藉由排汗、大小便，甚至呼吸而流失。
While these functions are essential to our survival, we need to compensate for the fluid loss.
然而这些功能对我们生存又很重要，所以我们需要弥补流失的体液。
Maintaining a balanced water level is essential to avoid dehydration or over-hydration,
维持体内水分平衡是必要的，以避免脱水或体内水分过多，
both of which can have devastating effects on overall health.
两者皆会对整体健康造成严重的影响。
At first detection of low water levels, sensory receptors in the brain's hypothalamus signal the release of antidiuretic hormone.
体内开始侦测到水分过低时，脑部下视丘的感应接收器就会发出讯号，通知释放抗利尿激素／ADH。
When it reached the kidneys, it creates aquaporins,
当ADH抵达肾脏时会造成水孔蛋白，
special channels that enable blood to absorb and retain more water, leading to concentrated, dark urine.
一种特殊的通道使血液吸收并保留更多水分，造成浓缩及深褐色的尿液。
Increased dehydration can cause notable drops in energy, mood, skin moisture, and blood pressure, as well as signs of cognitive impairment.
脱水加重会造成明显的精力减退、心情不振、皮肤变干、低血压以及认知障碍的症状。
A dehydrated brain works harder to accomplish the same amount as a normal brain,
脱水的脑会比正常的脑更难完成同等份量的工作，
and it even temporarily shrinks because of its lack of water.
甚至会因为缺水而暂时萎缩。
Over-hydration, or hyponatremia, is usually caused by overconsumption of water in a short amount of time.
体内水分过多，也就是低钠血症，通常是因为短时间内摄取过多水分造成的。
Athletes are often the victims of over-hydration because of complications in regulating water levels in extreme physical conditions.
运动员是较常见体内过多水分的受害者，因为在极端的身体状况下，难以调节水分所导致脑部脱水会使ADH分泌增加。

Whereas the dehydrated brain amps up the production of antidiuretic hormone,
反之，过多水分的脑
the over-hydrated brain slows, or even stops, releasing it into the blood.
会使ADH释放到血液变慢，甚至停止。
Sodium electrolytes in the body become diluted, causing cells to swell.
体内的电解质钠被稀释，造成细胞水肿。
In severe cases, the kidneys can't keep up with the resulting volumes of dilute urine.
严重的情况下肾脏会无法负荷大量被稀释的尿液。
Water intoxication then occurs, possibly causing headache, vomiting, and, in rare instances, seizures or death.
水中毒随之而发生可能导致头痛、呕吐，少数严重者甚至会痉挛或死亡。
But that's a pretty extreme situation.
但那是一种非常极端的状况。
On a normal, day-to-day basis, maintaining a well-hydrated system is easy
在一般日常生活中保持体内水平衡非常容易
to manage for those of us fortunate enough to have access to clean drinking water.
对我们这些相当幸运可以取得干净饮水的人而言。
For a long time, conventional wisdom said that we should drink eight glasses a day.
长久以来，一般观念都认为我们每天要喝8杯水，
That estimate has since been fine-tuned.
但这个数据已被重新调整过。
Now, the consensus is that the amount of water we need to imbibe depends largely on our weight and environment.
现在的共识是我们需要摄取的水量主要取决于我们的体重及环境。
The recommended daily intake varies from between 2.5-3.7 liters of water for men, and about 2-2.7 liters for women,
建议男性每日水分摄取量在2.5-3.7公升之间，女性则在2-2.7公升之间，
a range that is pushed up or down if we are healthy, active, old, or overheating.
范围可弹性调整，依照我们是否健康、运动、年老或是否过热来判断。
While water is the healthiest hydrator, other beverages, even those with caffeine like coffee or tea, replenish fluids as well.
虽然水是最健康的饮品，但其他饮料，甚至含有咖啡因的咖啡及茶也都可以补充体液。
And water within food makes up about a fifth of our daily H20 intake.
食物所含的水约可补充我们每日水分摄取量的1/5。
Fruits and vegetables like strawberries, cucumbers, and even broccoli are over 90% water,
水果及蔬菜--像是草莓、小黄瓜，甚至是花椰菜皆含有超过90%的水分，
and can supplement liquid intake while providing valuable nutrients and fiber.
在提供有用的营养及纤维同时也能补充液体的摄取。
Drinking well might also have various long-term benefits.
良好的饮水习惯也会带来许多长远的效益。
Studies have shown that optimal hydration can lower the chance of stroke, help manage diabetes,
研究显示理想的水分摄取可以降低中风的机率，协助控制糖尿病，
and potentially reduce the risk of certain types of cancer.
也可能降低某些癌症的风险。
No matter what, getting the right amount of liquid makes a world of difference in how you'll feel, think, and function day to day.
不管如何，摄取适当的液体量，你身体的感受、思考及日常作业将会有很大的改善。