Which of the following is listed as a major water pollutant?

• A. Untreated Sewage
• B. Clean Water
• C. Oxygen
• D. Minerals

Answer: (A)

Water pollution happens when contaminants are introduced into water bodies, changing quality and harming living things. Untreated sewage stands out as a major pollutant because it brings a large amount of organic matter and disease-causing microbes into the water. The high organic load increases biological oxygen demand, which uses up dissolved oxygen and can create dead zones where fish and other aquatic life cannot survive. It also carries pathogens that can spread illness to people who use the water.

Clean water isn’t a pollutant, so it wouldn’t be listed as a major pollutant. Oxygen itself is essential for aquatic life, and while low oxygen levels can be a problem, oxygen gas isn’t classified as a pollutant. Minerals can be natural components of water and aren’t singled out here as the major pollutant; in some cases, certain minerals can be harmful in very high concentrations, but they’re not the example given.