Which sampling method is primarily used for monitoring lead and copper levels?

First draw sampling is the selected method for monitoring lead and copper levels primarily because it effectively captures the concentration of these contaminants when water sits in the plumbing system over time. This method involves taking the first water that comes out of the tap after a period of inactivity, typically at least six hours.

The rationale behind this approach is that lead and copper can leach into drinking water from plumbing materials, especially when water is stagnant. By taking the first draw, this sampling method ensures that the sample reflects the highest potential concentration of these metals, which can indicate the presence of lead service lines or copper plumbing that may be contributing to contamination.

This method is particularly important for regulatory compliance under the Lead and Copper Rule, as it allows for the accurate assessment of potential risks to public health associated with lead and copper in drinking water.