What is a primary component of a well that prevents surface contaminants from entering?

The annular seal is designed to create a barrier between the well and the surrounding surface environment. It is typically made of grouted material that encases the well casing in the area where the well passes through the soil or rock. This seal is vital in preventing surface contaminants, such as bacteria, chemicals, and other pollutants, from seeping into the well and compromising the water quality. It ensures that water drawn from the well remains safe for consumption by protecting it from external factors.

In contrast, the well screen is primarily used to allow water to enter the well while filtering out sand and sediment, making it less focused on contaminant prevention from the surface. The well cap serves to close off the top of the well and prevent debris or animals from entering but does not offer the comprehensive protection against surface contamination that an annular seal provides. The pressure tank is a component related to the water delivery system within a household, not a protective measure against contamination.