Water sampling from residential taps should be collected after which condition to ensure the sample is representative?

• A. Residential tap most commonly used for drinking water after the water has remained motionless for 6 hours
• B. Any tap in the home
• C. Public drinking fountain
• D. Bathroom sink

Answer: (A)

Representing typical exposure requires the sample to come from the tap that is normally used for drinking, and after the water has been still in the plumbing for several hours. This stagnation period allows lead that may be present in pipes, solder, or fixtures to dissolve into the water that resides in contact with the interior surfaces, giving a sample that reflects what a resident would actually drink. Sampling from a tap that isn’t used for drinking, or from places like a bathroom sink or a public drinking fountain, can give concentrations that don’t represent usual household drinking water because those taps may have different materials, flow patterns, or stagnation histories.