**Core Concept**
The lining of an open sanitary well is a critical aspect of preventing contamination and ensuring the safety of the water supply. The lining serves as a barrier to prevent the entry of pathogens, sediments, and other contaminants into the well. A minimum depth extension of the lining is essential to prevent the leakage of contaminants into the well.

**Why the Correct Answer is Right**
The correct answer is based on the principle of ensuring a sufficient barrier between the well and the surrounding environment. The lining of the well should extend to a minimum depth to prevent the seepage of surface water, which can contain pathogens and other contaminants, into the well. This is particularly important in areas with high water tables or where the surrounding soil is permeable. The lining should be designed to prevent any potential pathways for contamination, thereby ensuring the quality and safety of the water supply.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is likely incorrect because it may not provide sufficient protection against contamination. A lining depth of 0 meters would essentially mean that the well is not lined at all, which would be a significant risk to the water quality.

**Option B:** This option may be incorrect because it does not take into account the local hydrogeological conditions. The minimum depth extension of the lining should be determined based on the specific site conditions, including the water table, soil type, and surrounding geology.

**Option C:** This option is likely incorrect because it may be too shallow to provide adequate protection against contamination. A lining depth of 1 meter may not be sufficient to prevent the seepage of surface water into the well.

**Option D:** This option is likely incorrect because it is too vague and does not provide a specific depth extension. A lining depth of "as required" may not be sufficient to ensure the quality and safety of the water supply.

**Clinical Pearl / High-Yield Fact**
The lining of an open sanitary well should extend to a minimum depth of 1.5 to 2 meters below the ground surface to prevent contamination and ensure the safety of the water supply. This is a critical aspect of well construction and maintenance, and failure to do so can have serious consequences for public health.

**Correct Answer:** C.