David Cyle, age 12, of Atlanta, Georgia, for his question:

What is a water table?

Tables are famous for their flat tops, so are quiet ponds and calm, unruffled lakes. However, a water table is underground and its top may be as level as a table top, or it may be tilted. It is there because a lot of rains and melted snows sink down into the ground. Below the surface, layers of hard and soft minerals form thick rocky sandwiches, often cracked and tilted with jumbled fragments. Soggy rains seep down the cracks, settle in the pockets of porous rocks and rest on top of dense, solid slabs. All these buried reservoirs are called ground water. The top of the ground water is called the water table. And a lot depends upon it. If it happens to be very far below the surface, the trees cannot dip down their roots and tap its moisture. In a long dry season, there is less ground water and the water table sinks. Wells dip down into the buried reservoirs and the moisture seeps in to fill them as high as the water table. When the water table sinks, the well may run dry.