When measuring the water temperature at a faucet for sampling, where should the thermometer probe be placed?

The correct approach for measuring the water temperature at a faucet for sampling is to place the thermometer probe before the sample is collected. This ensures that the temperature measured accurately reflects the temperature of the water as it exits the faucet, providing a precise reading prior to any potential cooling or alteration that may occur when water is allowed to flow or when a sample is drawn.

By taking the temperature before sampling, it eliminates variables that might affect the temperature reading. The temperature at the point of collection is critical in assessing conditions that favor the growth of Legionella, as certain temperature ranges are more conducive to this bacteria. Accurate temperature measurements allow for better evaluation of the plumbing system's risk factors.

If the thermometer were placed in the stream of water after a sample is collected, it could provide an inaccurate temperature reading influenced by the cooling effect of the sample container or air exposure, rather than the actual water temperature. Placing the probe above or below the stream of water similarly fails to capture the true temperature at the point of interest in the water delivery system.