Two parts hydrogen and one part
oxygen (H2O), water is the most abundant substance in the human
body, accounting for up to 60 percent of our body weight. Even though water
has no calories or other nutrients, we can go for only a few days without
it. In contrast, a healthy person can survive for 6 to 8 weeks without food.
A loss of only 5 to 10 percent of body water results in serious dehydration,
while a 15 to 20 percent loss is usually fatal.
Water is essential to virtually
every body function, including digestion, absorption, and transport of
nutrients elimination of body waste, and regulation of body temperature, as
well as many other chemical processes. It provides a protective cushion for
body cells, and in the form of amniotic fluid protects a developing fetus.
Water is needed to build all body tissues and is the base of all blood and
fluid secretions such as tears, saliva, and gastric juices, as well as the
fluids that lubricate our organs and joints. it also keeps our skin soft and
As our body ages, it becomes
dryer. The body of a newborn infant is 75 to 80 percent water, compared to
50 percent after age 65 or 70. This drying out is reflected in the wrinkled
skin, reduced saliva flow, and stiffened joints that occur naturally with
How much do we need ?
The human body needs enough water
to ensure that the urine is pale, not dark or bright yellow. For the average
adult this may translate to six to eight glasses of water a day. Most of
this comes from drinks -- plain water, coffee, tea, juices, soft drinks --
but surprisingly there's a substantial amount in foods as well. Fruits and
vegetables, for example, are 70 to 95 percent water, compared to 75 percent
of an egg, 40 to 60 percent of meat, poultry, and fish, and 35 percent of
Our daily needs vary a lot. We
need more water in hot weather, during exercise, or when we have a fever,
cold, or other illness. We also need more during pregnancy to provide for
the amniotic fluid and the expanded blood volume, as well as to meet the
needs of the developing fetus. Nursing mothers need to increase their fluid
intake to produce milk, which is 87 percent water.
As a general rule, the amount of
water we take in should be equal to what is excreted. Many factors can
affect this balance. For example, taking diuretics or other drugs that
increase urination increases our needs for fluids. Drinking large amounts of
tea or coffee has a similar diuretic effect, which can offset the fluid
intake from these drinks. And eating salty foods also increases our need for
extra water to maintain proper fluid balance.
Thirst decreases with age, so
older people should drink water often even if they don't feel thirsty. As
well, thirst may lag behind the body's need for water during intense
exercise or when it's extremely hot and humid. By the time you feel thirsty,
you may already be dehydrated. If you drink more fluid than you need, the
kidneys excrete the excess by increasing the volume of urine. If you drink
more water than the kidneys can handle, excess is absorbed by your cells.
Arsenic in drinking water
Arsenic gets into our ground
water supply when mineral deposits or rocks containing arsenic dissolve.
Also, through the discharge of industrial wastes, and as fallout from the
burning of fossil fuels -- especially coal. Although the United States and
Canadian governments have set strict standards that allow only minute trace
amounts of arsenic in our drinking water, the International Agency for
Research on Cancer considers arsenic a human carcinogen, and years of
consumption of drinking water containing arsenic at levels close to, or
higher than the guideline values have been found to crease the risk of skin
cancer, as well as tumors of the bladder, kidney, liver, and lung. Long-term
exposure to higher levels of arsenic in drinking water may also cause
abnormal heart rhythm and blood vessel damage, decreased production of red
blood cells, and thickening and discoloration of the skin. Again, if you
have concerns, have your water tested, and consider investing in an in-home
water treatment device to reduce the arsenic level in your water supply.