The correct answer is C. Measuring the depth of water in the well.
A well is a hole in the ground that is dug or drilled to reach groundwater. The depth of the water in a well can be measured by lowering a tape measure or a sounding line into the well. The depth of the water table is the level at which the ground is saturated with water. The water table is usually located below the surface of the ground, but it can be found at or near the surface in some areas. The depth of the water table can vary depending on the amount of rainfall, the type of soil, and the slope of the land.
Option A is incorrect because looking through a well will not provide any information about the depth of the water table. Option B is incorrect because standing on a well will not provide any information about the depth of the water table. Option D is incorrect because measuring the depth of water in a well is the only way to determine the depth of the water table.