What does pollution refer to?

Pollution refers to the introduction of foreign substances into an environment, in this context, water, that can have harmful effects on living organisms and the ecosystem as a whole. This typically includes contaminants like chemicals, waste products, and harmful microorganisms. The presence of these pollutants alters the natural biological and chemical composition of the water, leading to detrimental impacts on fish, plants, and other aquatic life.

By contrast, the other options describe processes or methods that do not align with the definition of pollution. For example, evaporating water is a natural process that does not introduce harmful substances, while natural occurrences that purify water are processes that actually clean rather than contaminate. A method to filter and clean drinking water involves actively removing pollutants, making it the opposite of what pollution represents. Thus, option B accurately encapsulates the essence of pollution as it pertains to water quality and its impact on the environment and organisms.