Abstract
Today, at least one-fifth of all people worldwide lack access to safe drinking water, a problem that will almost certainly worsen as the earth's population grows. Although the vast majority of industrial discharges into waterways are regulated and treated, and most cities and towns effectively monitor and treat their sewage for chemical contaminants, problems such as arsenic contamination and dangerous microorganisms still trouble public water supplies in wealthy nations. In developing countries, most cities discharge 80-90% of their untreated sewage directly into rivers and streams, which are used for drinking, bathing, and washing. This lack of sewage treatment has allowed dangerous microorganisms to spread, posing one of the greatest threats to human health in the developing world: waterborne diseases caused by deadly microbes in water. Contamination isn't the only problem: in many areas of the world, drinkable water is a scarce resource available to many only at high cost, when it is available at all.