Which water quality parameters must be immediately tested in the field after sample collection?

The parameters that must be immediately tested in the field after sample collection include chlorine residual, pH, and temperature due to their critical roles in assessing water quality and potential contamination.

Chlorine residual is essential because it indicates whether there is enough chlorine remaining in the water to disinfect effectively and combat pathogens. pH is vital as it affects many chemical and biological processes in water, including the solubility of nutrients and the effectiveness of disinfectants. Temperature is also significant because it influences reactions in the water, including microbial activity and the stability of certain compounds.

Testing these parameters in the field ensures that the results are accurate and representative of the water quality at the time of sampling. Delaying these tests could lead to degradation of the sample or changes in quality that might mask contamination or treatment failures.

In contrast, other options include parameters like turbidity, color, or conductivity, which, while important for overall water quality assessments, do not require immediate field testing like chlorine residual, pH, and temperature do. Turbidity and color can often be assessed later, as they are less sensitive to changes over short periods compared to the immediate needs addressed by the first set of parameters.