Which is the best definition of turbidity in water?

Turbidity in water is best defined as anything in water that scatters light. This definition captures the essence of turbidity, as it describes the cloudiness or haziness experienced when particles are suspended in water, leading to the scattering of light. The presence of these particles can originate from various sources, including sediment, algae, organic matter, and other pollutants.

Understanding turbidity is important because it affects water quality and can indicate the presence of harmful substances. High turbidity can inhibit the penetration of sunlight in water bodies, affecting aquatic life, and may also indicate that pathogens or other contaminants are present.

The other options provided do not comprehensively define turbidity. Sequestered iron and manganese particles specifically describe certain dissolved metals rather than the general scattering of light by various particles. The amount of dissolved material in water pertains more to total dissolved solids, which does not directly relate to the scattering of light. Lastly, the combined optical effect of pH, chlorine, and color involves specific chemical parameters and interactions but does not adequately define turbidity itself. Thus, the answer that captures the full definition of turbidity is the one stating that it is anything in water that scatters light.