>> Think back on the ways you've probably used water today already. Apart from cooking
or mopping the floors, think about how you used water to care for your personal body.
I'd like to share with you how I used water already. I got a drink of water when I first
got up this morning. I used water to cleanse my toothbrush, to brush my teeth, and to rinse
out my mouth. I used lots of water to shower with and to wash my hair. Then I used water
in the sink to shave my face and a little bit to smooth back my hair. When I went to
the toilet, it was water that carried away the waste down a tube somewhere far out of
sight and out of mind. And then after the toilet, I washed my hands with soap in the
sink. Water is necessary in each of these instances to either replenish my body with
fluids, to wash away the wastes from my body, or to keep my body free from germs--these
three categories of health, sanitation, and hygiene. Water is also used for cosmetic purposes
when I shave or wet my hair to keep it in place.
In fact, regarding health, men need to consume about 3.7 liters a day, or about a gallon
of water, and women need to consume about three quarters of a gallon. About 70-75% of
our human body weight is water. The blood is 82% water, human brain is 85% water. And
it is no wonder that some of the early symptoms of dehydration are fuzzy short-term memory,
trouble with basic math, or difficulty in focusing on small print because your eyes
use a lot of fluids to do their work. What does water do in and for the body, we should
ask. Well, it serves as lubricant. It forms the base for saliva. It forms fluid that surrounds
the joints. It regulates the body temperature, for example, through perspiration. It helps
to alleviate constipation by moving food through the intestinal tract and eliminating waste
products, so it's a very fine detox agent. And finally, it regulates metabolism, that
is, how our body gets energy from its food. So our thirst is a natural signal to our body
that it needs water. And when people don't get enough clean water to drink, they will
drink the only other water they can get, dirty water.
Water is used to do two things regarding sanitation: to dilute the waste and to move it to a place
where it can be treated. For many centuries before there were very many people on the
planet, human and animal body, bodily waste could be released into a river or stream.
When the waste is sufficiently small, the water has enough volume to dilute the waste
and render it harmless to people who might be living downstream. The world and the amount
of water it contains has and will forever be the same. It will not increase. But as
populations have increased, it has become much more difficult to find enough water to
dilute waste sufficiently. This is especially true in the industrial or developed world
with people moving into larger and larger cities, as you heard during the last lecture
about London, Chicago, and Milwaukee.
Well, this brings us to the second usage of water in sanitation: to carry it away to a
place for it to be treated or disposed of. A very old system still in use today is called
the septic tank and system. The water carries the waste by gravity from the home to an enclosed
tank. There the solids will settle to the bottom, and the liquid water flows out the
top of the tank into a drain field where it percolates into the soil. There natural bacteria
in the waste and in the soil have time to degrade the waste and make it more inert or
safe. Septic systems can be very effective ways of using water to transport wastes, but
only in places where population densities are small and there is plenty of land for
the water to be spread out. A more modern system and one that's used in large developed
cities is one in which water is used to carry the waste to a centrally located waste treatment
plant or called a wastewater treatment plant. And there in the treatment plant natural processes
are mimicked using engineered systems, in effect, doing the same thing that the bacteria
would do in nature in that soil that we spoke about, but in a more controlled and speedier
fashion. Then once treated, that water can be rereleased into a river or a lake or a
stream where it will not have an adverse affect on either ecology of the water body or people
living downstream of it.
The third important category is hygiene. It refers to those practices that we do to maintain
and preserve our health. Specifically, hygiene in the home and everyday life settings plays
an important part in preventing the spread of infectious diseases. Now many of these
practices require water: hand washing, as we've mentioned, hand washing in the sink,
proper rinsing of food, care and cleaning of domestic animals, and other practices that
are generally considered proper hygiene, including bathing regularly, washing scalp hair, keeping
hair short, wearing clean clothing, and brushing one's teeth. Some practices are even gender
specific, such as those used by a woman during her menstrual cycle. Hand washing is probably
the most important single behavior that can be implemented in a developing country to
reduce the risk of infectious diseases. Recall how every hospital has numerous hand washing
stations throughout the patient care floors and visitors are required to wash their hands
before entering a patient's room. Let's take a look at what is often called the F diagram.
The F diagram shows various pathways that pathogenic or disease-causing bacteria can
take from feces to future victim—that is, you or me. The fecal material if it is not
deposited in an isolated place such as latrine or toilet can easily find its way into water,
into fields where crops are grown, or fingers of children who are playing. Finally, flies
often carry bacteria from the feces to your food, which is why we often cover our food.
Some of these pathways lead directly to your mouth, as when you drink contaminated water
or touch your dirty fingers to your mouth, or they lead to your food, which of course
leads to your mouth. Once in your mouth, you are at increased risk for the diseases that
these pathogenic bacteria will carry. It has been estimated that almost 1/10 of the global
disease burden, the total global disease burden, could be prevented by improving water supply,
sanitation, hygiene, and management of water resources. That's all diseases. Childhood
underweight causes about 35% of all deaths of children under the age of five. An estimated
50% of this underweight or malnutrition is associated with repeated diarrhea or intestinal
nematode infections as a result of unsafe water. Such underweight in children is directly
responsible for about 70,000 deaths per year. But we'll talk more about these diseases in
the next lecture.