Which of the following is a common contaminant in untreated water?

The presence of pathogens and particles in untreated water is a significant concern for public health. Untreated water sourced from rivers, lakes, or groundwater can harbor a variety of microorganisms, including bacteria, viruses, and parasites that can cause serious illnesses. These pathogens can originate from human and animal waste, making untreated sources particularly risky for consumption without proper treatment, such as disinfection or filtration.

In addition to biological contaminants, untreated water often contains particulates such as sediment, organic matter, and other debris, which can further pose health risks if ingested, as well as degrade the quality of the water for other uses. The risk of contamination from these sources underscores the importance of water treatment processes, including filtration and disinfection, to ensure safe drinking water.

Other options, while related to water quality, do not represent common contaminants in untreated water. Chlorine is typically used in water treatment to disinfect, not found in untreated water. Lead can be a contaminant in drinking water but is primarily a concern from plumbing system leaks or corrosion, not from the natural state of untreated water. Oxygen, while essential for life and present in all forms of water, is not considered a contaminant. Thus, pathogens and particles are the most prevalent and concerning contaminants found in untreated