Well water contamination from surface water can be prevented by using a ______.

Using a casing is an effective method to prevent well water contamination from surface water. A casing is a protective tube installed in the well to create a barrier that separates the groundwater from potential contaminants found in surface water. This casing extends from the well head down into the earth, providing a shield against pollutants that may seep into the well from the surface.

The proper casing installation ensures that the well is properly sealed and extends above the ground level, which helps to prevent surface runoff from entering the well. This is critical for maintaining the quality of the groundwater and ensuring it remains safe for consumption.

The other options, while they may contribute to water quality management in different contexts, do not specifically address the problem of surface water contamination as effectively as a casing does.