Which of the following is a main component of a water well system?

The wellhead is an essential component of a water well system, serving as the entry point for water to be extracted from the aquifer below. It is crucial because it protects the well from contamination and prevents surface water from entering the well. The wellhead includes various fittings and devices such as the casing, which keeps the well structure intact, and the sealing mechanisms that ensure no contaminants can enter.

In contrast, while other options like a water pump station, filtration tank, and water storage reservoir play significant roles in managing and delivering water, they are not foundational components of the well system itself. The water pump is responsible for lifting the water to the surface, the filtration tank helps in treating the water, and the storage reservoir is used for storing water for future use; however, all these components depend on the well and its wellhead for access to the groundwater supply. Therefore, understanding the wellhead's role emphasizes its importance as the starting point of the well system.