Well casing is a protective tube installed in a drilled well to prevent the surrounding soil and rock from collapsing into the well. It also helps to keep contaminants from entering the water supply. The casing is typically made of steel or PVC and is placed in the well after drilling is complete. The casing is secured in place with cement, which fills the space between the casing and the well walls. This process, known as cementing, ensures the structural integrity of the well and maintains the quality of the water. Proper installation of well casing is essential for safe and effective groundwater extraction.