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Take a look at the water in this glass.

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Refreshing, hydrating, and invaluable
to your survival.

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Before you take a sip, though,

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how do you know that the water inside
is free from disease-causing organisms

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and pollutants?

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One out of ten people in the world
can't actually be sure

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that their water is clean 
and safe to drink.

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Why is that?

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Inadequate sanitation,

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poor protection of drinking water sources,

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and improper hygiene

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often lead to sewage 
and feces-contaminated water

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That's the ideal breeding ground
for dangerous bacteria,

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viruses,

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and parasites.

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And the effects of these pathogens
are staggering.

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Diarrheal disease from unsafe water is one
of the leading causes of death

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around the world for children under five.

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And according to a U.N. report from 2010,

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microbial water-borne illnesses killed
more people per year than war.

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Proper treatment processes, though,
can address these threats.

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They usually have three parts:

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sedimentation,

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filtration,

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and disinfection.

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Once water has been collected
in a treatment facility,

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it's ready for cleaning.

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The first step, sedimentation,
just takes time.

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The water sits undisturbed, allowing
heavier particles to sink to the bottom.

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Often, though, particles 
are just too small

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to be removed by sedimentation alone

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and need to be filtered.

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Gravity pulls the water downward through
layers of sand

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that catch leftover particles 
in their pores,

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prepping the water 
for its final treatment,

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a dose of disinfectant.

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Chemicals, primarily forms 
of chlorine and ozone,

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are mixed in to kill off any pathogens

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and to disinfect pipes 
and storage systems.

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Chlorine is highly effective in destroying
water's living organisms,

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but its use remains government-regulated

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because it has potentially harmful
chemical byproducts.

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And if an imbalance of chlorine occurs
during the disinfection process,

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it can trigger other chemical reactions.

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For example, 
levels of chlorine byproducts,

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like trihalomethanes, could skyrocket,
leading to pipe corrosion

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and the release of iron, copper,
and lead into drinking water.

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Water contamination from these
and other sources

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including leaching,

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chemical spills,

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and runoffs,

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has been linked 
to long-term health effects,

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like cancer,

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cardiovascular and neurological diseases,

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and miscarriage.

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Unfortunately, analyzing the exact risks

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of chemically contaminated 
water is difficult.

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So while it's clear that disinfectants
make us safer

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by removing disease-causing pathogens,

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experts have yet 
to determine the full scope

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of how the chemical cocktail 
in our drinking water

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really impacts human health.

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So how can you tell whether the water
you have access to,

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whether from a tap or otherwise,

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is drinkable?

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Firstly, too much turbidity,

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trace organic compounds,

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or high-density heavy metals like arsenic,
chromium, or lead,

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mean that the water 
is unsuitable for consumption.

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A lot of contaminants, 
like lead or arsenic,

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won't be obvious without tests,

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but some clues, like cloudiness,

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brown or yellow coloration,

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a foul odor,

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or an excessive chlorine smell

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can indicate the need 
to investigate further.

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Water testing kits can go a step further

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and confirm the presence of many different
contaminants and chemicals.

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With many types of contamination,

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there are ways of treating water where 
it's used instead of close to its source.

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Point-of-use treatment has actually
been around for thousands of years.

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Ancient Egyptians boiled away many
organic contaminants with the sun's heat.

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And in Ancient Greece, Hippocrates
designed a bag

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that trapped bad tasting 
sediments from water.

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Today, point-of-use processes usually
involve ionization

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to lower mineral content.

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They also use adsorption filtration,

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where a porous material
called activated carbon

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strains the water to remove contaminants
and chemical byproducts.

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While it's not always an effective
long-term solution,

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point-of-use treatment is portable,
easy to install, and adaptable.

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And in regions where large-scale
systems are unavailable,

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or where water has been contaminated
further along its journey,

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these systems can mean the difference
between life and death.

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Clean water remains a precious
and often scarce commodity.

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There are nearly 800 million of us who
still don't have regular access to it.

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The good news is that continued
developments in water treatment,

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both on a large and small scale,

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can alleviate a lot of unsafe conditions.

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Implementing proper systems where
they're needed

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and paying careful attention
to the ones already in place

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will fulfill one of the most basic
of our human needs.