Answer to Question 1
More than two-thirds of the earth's surface is covered by water. Water is continually cleansing itself by evaporating, forming clouds, and raining back to the earth. Unfortunately, people are contaminating the water supply faster than it can cleanse itself. As the population grows in a particular area, so does industry, which pours into the water a vast array of contaminants: detergents, sulfuric acid, lead, hydrofluoric acid, ammonia, and so on. Increased agricultural production also pollutes water with insecticides, herbicides, and nitrates (from fertilizers). The result is the spread of pollution in creeks, streams, and lakes; along coastlines; and-most seriously-in groundwater, where purification is almost impossible. Water pollution poses the threat of disease epidemics such as hepatitis and dysentery as well as poisoning by exotic chemicals. Some rivers and lakes are now so polluted that they cannot support fish and other organisms that require relatively clean, oxygen-rich water. These lakes and rivers are accurately described as dead. Human waste is also a major contributor to water pollution. An even bigger source of pollution is waste from oil refining, food processing, animal feedlots, textile and paper manufacturing, and other industries.
Answer to Question 2
a
Water-bottle
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Water strider (Gerris remigis) on water surface, showing surface tension.