What type of casings must be fitted with suitable packers or sealing material?

The inner casing must be fitted with suitable packers or sealing material because it is crucial for preventing contamination of the groundwater and ensuring the integrity of the well. The primary function of the inner casing is to protect the well from surface contaminants and to maintain the flow of water. By using suitable packers or sealing materials, the inner casing creates a barrier that helps seal the wellbore against groundwater ingress or egress, which is essential for maintaining water quality and well function.

Other types of casings, such as outer casings, may not require the same type of sealing interventions since they are usually installed to provide structural support and to separate the well from the surrounding geological formations. Temporary casings are often used during drilling operations to provide support but may not be designed for long-term sealing. Plastic casings serve specific functions but might not necessitate the same level of sealing as an inner casing, especially concerning groundwater protection. Thus, inner casings are specifically highlighted for their role in requiring appropriate sealing measures.