Placeholder Image

Subtitles section Play video

  • Take a look at the water in this glass.

  • Refreshing, hydrating, and invaluable to your survival.

  • Before you take a sip, though,

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

  • and pollutants?

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

  • that their water is clean and safe to drink.

  • Why is that?

  • Inadequate sanitation,

  • poor protection of drinking water sources,

  • and improper hygiene

  • often lead to sewage and feces-contaminated water

  • That's the ideal breeding ground for dangerous bacteria,

  • viruses,

  • and parasites.

  • And the effects of these pathogens are staggering.

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

  • around the world for children under five.

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

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

  • Proper treatment processes, though, can address these threats.

  • They usually have three parts:

  • sedimentation,

  • filtration,

  • and disinfection.

  • Once water has been collected in a treatment facility,

  • it's ready for cleaning.

  • The first step, sedimentation, just takes time.

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

  • Often, though, particles are just too small

  • to be removed by sedimentation alone

  • and need to be filtered.

  • Gravity pulls the water downward through layers of sand

  • that catch leftover particles in their pores,

  • prepping the water for its final treatment,

  • a dose of disinfectant.

  • Chemicals, primarily forms of chlorine and ozone,

  • are mixed in to kill off any pathogens

  • and to disinfect pipes and storage systems.

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

  • but its use remains government-regulated

  • because it has potentially harmful chemical byproducts.

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

  • it can trigger other chemical reactions.

  • For example, levels of chlorine byproducts,

  • like trihalomethanes, could skyrocket, leading to pipe corrosion

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

  • Water contamination from these and other sources

  • including leaching,

  • chemical spills,

  • and runoffs,

  • has been linked to long-term health effects,

  • like cancer,

  • cardiovascular and neurological diseases,

  • and miscarriage.

  • Unfortunately, analyzing the exact risks

  • of chemically contaminated water is difficult.

  • So while it's clear that disinfectants make us safer

  • by removing disease-causing pathogens,

  • experts have yet to determine the full scope

  • of how the chemical cocktail in our drinking water

  • really impacts human health.

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

  • whether from a tap or otherwise,

  • is drinkable?

  • Firstly, too much turbidity,

  • trace organic compounds,

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

  • mean that the water is unsuitable for consumption.

  • A lot of contaminants, like lead or arsenic,

  • won't be obvious without tests,

  • but some clues, like cloudiness,

  • brown or yellow coloration,

  • a foul odor,

  • or an excessive chlorine smell

  • can indicate the need to investigate further.

  • Water testing kits can go a step further

  • and confirm the presence of many different contaminants and chemicals.

  • With many types of contamination,

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

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

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

  • And in Ancient Greece, Hippocrates designed a bag

  • that trapped bad tasting sediments from water.

  • Today, point-of-use processes usually involve ionization

  • to lower mineral content.

  • They also use adsorption filtration,

  • where a porous material called activated carbon

  • strains the water to remove contaminants and chemical byproducts.

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

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

  • And in regions where large-scale systems are unavailable,

  • or where water has been contaminated further along its journey,

  • these systems can mean the difference between life and death.

  • Clean water remains a precious and often scarce commodity.

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

  • The good news is that continued developments in water treatment,

  • both on a large and small scale,

  • can alleviate a lot of unsafe conditions.

  • Implementing proper systems where they're needed

  • and paying careful attention to the ones already in place

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

Take a look at the water in this glass.

Subtitles and vocabulary

Operation of videos Adjust the video here to display the subtitles

B2 H-INT US TED-Ed water chlorine treatment chemical contaminated

【TED-Ed】When is water safe to drink? - Mia Nacamulli

  • 14693 1410
    汪摳   posted on 2017/08/07
Video vocabulary