Subtitles section Play video Print subtitles 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.