When should first draw samples be collected?

First draw samples should be collected when taking lead and copper samples because this method ensures that the water drawn from the tap is representative of the water that has been sitting in the plumbing system. First draw samples are typically collected after the water has been stagnant for several hours, usually overnight, which allows for a more accurate representation of lead and copper concentrations that may leach from the pipes and fixtures. This is crucial for assessing potential health risks to consumers, as these metals can be harmful at certain levels.

Collecting these samples during routine cleaning of the water system, only during maintenance checks, or after a heavy rainfall would not provide reliable data on lead and copper concentrations because these activities may disturb the plumbing or introduce outside contaminants, thus compromising the integrity of the sample collected.