When should temperature and pH be measured?

• A. In the lab after analysis
• B. Immediately in the field after collection because they can change quickly
• C. Before collection
• D. Never measure

Answer: (B)

Temperature and pH are not fixed once water is collected; the sample can change quickly as it sits in a bottle or during transport. Measuring them in the field right after collection captures the water’s actual conditions at the time of sampling, which is essential for accurate interpretation and reliable QA/QC.

pH is influenced by temperature, and while portable meters offer temperature compensation, knowing the sample’s true temperature and reading pH immediately minimizes drift caused by CO2 exchange, microbial activity, or evaporation that can alter pH during storage. Field measurement ensures the data reflect what was present in the water when it was collected, not after it has sat for hours or days.

Measuring in the lab after analysis or never measuring would miss these changes and lead to results that don’t represent the sampled water. Measuring before collection isn’t possible because the sample isn’t there yet to test.