Which indicator would be least relevant in assessing water system performance?

External temperature is the least relevant indicator when assessing water system performance because it does not directly impact the operational efficiency or safety of the water distribution system. While temperature can influence certain aspects, such as the chemical reactions in water treatment processes or the growth of microorganisms, it does not provide concrete, immediate information regarding the functioning of the system itself.

In contrast, pressure levels are critical for ensuring adequate water delivery to consumers and detecting potential leaks. Water flow rates are essential for measuring the supply and demand balance within the system, indicating whether the system can meet its needs effectively. Contamination test results are vital for health and safety, as they directly assess the water quality and the risk posed to consumers. Hence, while temperature is a general environmental factor, it does not play a significant role in the performance analytics of a water system compared to the other indicators listed.