Concept:The water table is the upper surface of the zone of saturation, where all pore spaces in the ground are filled with water.
Explanation:A well will always contain water only when it is dug below the water table.
Above the water table is the zone of aeration, where pore spaces contain both air and water.
Below the water table is the zone of saturation, where all pore spaces and cracks are completely filled with groundwater.
When a well penetrates this saturated zone, water seeps into it from the surrounding rocks and soil.
This guarantees that the well will hold water at all times.
Digging above the water table would leave the well dry or with water only during rainy seasons.
Merely reaching a sand-bearing layer is not enough, because such a layer may lie above the water table and may not be fully saturated.
Therefore, the permanent availability of water in a well depends on its bottom being dug below the water table.
Answer:D. Below the water table