The drawdown of a well is determined by:

The drawdown of a well is defined as the difference between the static water level and the pumping water level during operation. When water is being extracted from a well, the water level drops, which creates a drawdown. The static water level is the height of the water in the well when no water is being pumped, while the pumping water level is measured when the well is actively being used. Understanding this difference is crucial for assessing the performance of a well and managing water resources effectively.

The other options, while related to well operation and measurement, do not define drawdown directly. A properly installed air line may be used for certain measurement purposes but does not convey the specific concept of drawdown. An electronic sounder assists in measuring water levels but does not determine drawdown without making the necessary comparison. Finally, a tape measure can be used to measure depths but similarly does not directly provide the drawdown figure without knowing both the static and pumping levels. Thus, defining drawdown through the difference between these two levels captures the essential concept accurately.