Which parameter requires a grab sample for testing?

pH is a water quality parameter that requires a grab sample for testing because it reflects the immediate acidity or alkalinity of the water at a specific point in time. The measurement of pH is sensitive to changes in conditions, such as temperature and the presence of other substances, making grab sampling the most accurate method to capture its current state.

In contrast, parameters like iron, nitrate, and zinc can sometimes be analyzed using composite samples, which collect water over a period of time to account for fluctuations in their concentrations. However, for instantaneous measurement, particularly for pH, the grab sample provides a direct and immediate assessment. This is crucial for maintaining the water quality and ensuring it meets regulatory standards.