According to the UN World Water Assessment Programme, about 2.3 billion people suffer from diseases associated with polluted water, and more than 5 million people die from these illnesses each year. Dysentery, typhoid, cholera, and hepatitis A are some of the ailments that result from ingesting water contaminated with harmful microbes. Other illnesses—such as malaria, filariasis, yellow fever, and sleeping sickness—are transmitted by vector organisms (such as mosquitoes and tsetse flies) that breed in or live near stagnant, unclean water.
A number of chemical contaminants—including DDT, dioxins, polychlorinated biphenyls (PCBs), and heavy metals—are associated with conditions ranging from skin rashes to various cancers and birth defects. Excess nitrate in an infant’s drinking water can lead to the “blue baby syndrome” (methemoglobinemia)—a condition in which the child’s digestive system cannot process the nitrate, diminishing the blood’s ability to carry adequate concentrations of oxygen.
Besides affecting human health, water pollution has adverse effects on ecosystems. For instance, while moderate amounts of nutrients insurface water are generally not problematic, large quantities of phosphorus and nitrogen compounds can lead to excessive growth of algae and other nuisance species. Known as eutrophication, this phenomenon reduces the penetration of sunlight through the water; when the plants die and decompose, the body of water is left with odors, bad taste, and reduced levels of dissolved oxygen.
Low levels of dissolved oxygen can kill fish and shellfish. In addition, aquatic weeds can interfere with recreational activities (such as boating and swimming) and can clog intake by industry and municipal systems. Some pollutants settle to the bottom of streams, lakes, and harbors, where they may remain for many years. For instance, although DDT and PCBs were banned years ago, they are still found in sediments in many urban and rural streams. They occur at levels harmful to wildlife at more than two-thirds of the urban sites tested. (Turk & Bensel, 2014)
Turk, J., & Bensel, T. (2014). Contemporary environmental issues (2nd ed.). San Diego, CA: Bridgepoint Education, Inc.