Which of the following is NOT a key factor monitored in surface water supplies?

Surface water supplies are carefully monitored for various key factors to ensure water quality and safety. Among these factors, disinfectant residuals, alkalinity, and total solids are critical for assessing the effectiveness of water treatment processes, water chemistry, and potential contaminants in the water source.

Disinfectant residuals are monitored to ensure that adequate levels of disinfectants are present to prevent microbial growth and maintain water safety until it reaches consumers. Alkalinity is important as it reflects the water's capacity to neutralize acids, which can affect both water quality and the potential for corrosion in distribution systems.

Total solids give insights into the concentration of dissolved and suspended substances, which can impact water clarity, chemical balance, and potential treatment challenges.

Temperature, while it can influence certain chemical reactions and biological activity in the water, is not considered a key factor in the same way as the others for routine water monitoring in surface supplies. Its role is more indirect, as temperature can affect the solubility and behavior of other constituents.

Thus, the monitoring of temperature is less critical in comparison to disinfectant residuals, alkalinity, and total solids in the context of ensuring the immediate safety and quality of surface water supplies.