What is the difference between a composite sample and a grab sample?

A grab sample is characterized by the fact that it is a one-time collection of water from a specific location at a particular moment. This type of sampling is useful for analyzing the immediate condition of the water or for targeted assessments. In contrast, a composite sample involves the combination of multiple grab samples collected over time or from different locations to create a more representative picture of the water quality. This can help to account for variability and fluctuations in water quality that might occur due to changes in conditions, time of day, or other factors.

Thus, the distinction lies in how the samples are collected and used: grab samples provide isolated snapshots, while composite samples deliver a more comprehensive overview by integrating multiple data points. This method is particularly valuable for monitoring and assessing trends in water quality, making option B the correct answer.