Which of the following is not included in the nine contaminant groups?

Turbidity is considered a physical characteristic of water rather than a specific contaminant or group of contaminants. The nine contaminant groups typically consist of microorganisms, inorganic contaminants (like nitrates and nitrites), organic chemicals (including volatile organic chemicals), and certain radionuclides. These groups focus on substances that can pose health risks or adversely affect water quality. Turbidity, while it can indicate the presence of particulates and influence water clarity, does not fit into the same category of specific contaminants that have defined chemical properties or health guidelines. Its primary role is as a measure of the clarity of water rather than as a specific contaminant type.