What is a First Draw Sample in water testing?

A First Draw Sample refers specifically to the initial water that comes out of a tap after it has been sitting still for a period of time, usually six hours or more. This is important in water quality testing, particularly when assessing contaminants like lead or copper, because it is the water that has been in contact with the plumbing material for an extended time.

In this context, the purpose of collecting a First Draw Sample is to capture any contaminants that may leach from the pipes or fixtures into the water, as this unflushed water can contain higher concentrations of these substances. Therefore, allowing the water to stagnate for several hours before collecting this sample is a critical step in ensuring accurate and consistent results for analysis.

The other options, while related to water sampling, do not capture the essence of what a First Draw Sample is. For example, sampling at the highest flow rate or from multiple tap positions might provide different data but not necessarily the baseline contaminants of concern that a First Draw Sample is specifically designed to measure. Similarly, samples taken after flushing the tap do not represent the contaminants that have accumulated while the water has been sitting in the plumbing system, thus invalidating the purpose of a First Draw Sample.