What is the minimum duration water should sit stagnant for a first-draw lead and copper sample collection?

The minimum duration for which water should sit stagnant before collecting a first-draw lead and copper sample is six hours. This duration is crucial because it allows lead and copper to leach from the plumbing into the stagnant water. When water remains in contact with the pipes for at least six hours, it simulates conditions that can lead to the buildup of these metals within the system.

This is particularly important for ensuring accurate testing results, as shorter stagnation periods may not capture the maximum concentration of lead and copper that could potentially leach from the plumbing. In many testing protocols, a six-hour stagnation period is often recommended to standardize sampling methods and ensure that the results are reflective of the worst-case scenario regarding contamination in the household plumbing.

The other options suggest either insufficient or excessive stagnation periods, which would not align with standard practices for accurately reflecting metal concentrations in water quality testing. Thus, adhering to the six-hour stagnation requirement is key to obtaining reliable data on lead and copper levels in drinking water.