Which factor must be analyzed immediately due to the lack of holding time?

The factor that must be analyzed immediately due to the lack of holding time is pH. This is because the pH level of water is sensitive to changes over time, particularly due to factors like temperature fluctuations, biological activity, and the introduction of contaminants. If a water sample is not analyzed promptly, its pH can shift significantly, which could lead to inaccurate results and potentially affect treatment processes or compliance with regulatory standards.

In contrast, while the other factors are important in water treatment, they do not exhibit the same level of immediate variability. Hardness and alkalinity can be measured with some flexibility in timing, as they tend to be more stable under normal conditions. Turbidity may change due to sedimentation or other environmental factors, but it is not as critical as pH when it comes to immediate analysis. Thus, prioritizing the analysis of pH is crucial for ensuring accurate and reliable water quality assessments.