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Water is virtually everywhere,

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from soil moisture and ice caps,

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to the cells inside our own bodies.

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Depending on factors like location,

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fat index,

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age,

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and sex,

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the average human is between 55-60% water.

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At birth, human babies are even wetter.

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Being 75% water, 
they are swimmingly similar to fish.

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But their water composition drops to 65%
by their first birthday.

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So what role does water 
play in our bodies,

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and how much do we actually need to drink
to stay healthy?

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The H20 in our bodies works to cushion
and lubricate joints,

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regulate temperature,

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and to nourish the brain and spinal cord.

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Water isn't only in our blood.

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An adult's brain and heart are almost
three quarters water.

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That's roughly equivalent to the amount
of moisture in a banana.

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Lungs are more similar to an apple at 83%.

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And even seemingly dry human bones
are 31% water.

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If we are essentially made of water,

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and surrounded by water,

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why do we still need to drink so much?

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Well, each day we lose two to three liters
through our sweat,

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urine,

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and bowel movements,

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and even just from breathing.

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While these functions 
are essential to our survival,

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we need to compensate for the fluid loss.

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Maintaining a balanced water level
is essential to avoid dehydration

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or over-hydration,

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both of which can have devastating
effects on overall health.

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At first detection of low water levels,

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sensory receptors 
in the brain's hypothalamus

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signal the release 
of antidiuretic hormone.

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When it reached the kidneys, 
it creates aquaporins,

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special channels that enable blood
to absorb and retain more water,

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leading to concentrated, dark urine.

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Increased dehydration can cause
notable drops in energy,

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mood,

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skin moisture,

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and blood pressure,

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as well as signs of cognitive impairment.

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A dehydrated brain works harder 
to accomplish the same amount

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as a normal brain,

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and it even temporarily shrinks
because of its lack of water.

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Over-hydration, or hyponatremia,

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is usually caused by overconsumption
of water in a short amount of time.

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Athletes are often the victims 
of over-hydration

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because of complications 
in regulating water levels

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in extreme physical conditions.

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Whereas the dehydrated brain amps
up the production of antidiuretic hormone,

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the over-hydrated brain slows,
or even stops, releasing it into the blood.

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Sodium electrolytes in the body
become diluted,

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causing cells to swell.

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In severe cases,

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the kidneys can't keep up with 
the resulting volumes of dilute urine.

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Water intoxication then occurs,

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possibly causing headache,

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vomiting,

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and, in rare instances, seizures
or death.

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But that's a pretty extreme situation.

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On a normal, day-to-day basis,

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maintaining a well-hydrated system
is easy to manage

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for those of us fortunate enough 
to have access to clean drinking water.

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For a long time, conventional wisdom said
that we should drink eight glasses a day.

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That estimate has since been fine-tuned.

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Now, the consensus is that the amount
of water we need to imbibe

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depends largely on our weight
and environment.

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The recommended daily intake varies from
between 2.5-3.7 liters of water for men,

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and about 2-2.7 liters for women,

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a range that is pushed up 
or down if we are healthy,

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active,

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old,

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or overheating.

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While water is the healthiest hydrator,

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other beverages,

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even those with caffeine 
like coffee or tea,

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replenish fluids as well.

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And water within food makes up 
about a fifth of our daily H20 intake.

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Fruits and vegetables like strawberries,

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cucumbers,

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and even broccoli are over 90% water,

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and can supplement liquid intake while
providing valuable nutrients and fiber.

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Drinking well might also have various
long-term benefits.

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Studies have shown that optimal hydration
can lower the chance of stroke,

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help manage diabetes,

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and potentially reduce the risk
of certain types of cancer.

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No matter what, getting the right amount
of liquid makes a world of difference

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in how you'll feel,

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think,

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and function day to day.