Historically, wells drilled were excavated under the water table by hand shovel until the incoming water reached the bailing capacity of the digger. To avoid collapse, the well was filled with blocks, bricks, tiles, or other material and capped with a cap of wood, stone, or concrete tile. Because of the type of construction, bored wells can go deeper beneath the water table than can hand-dug wells. Dug and bored wells are wide in diameter and expose the aquifer to a large area. Such wells can get water from less-permeable materials like very fine sand, silt, or clay. The disadvantages of this type of well are that they are shallow and lack continuous containment and grouting, making them susceptible to pollution from nearby surface sources, and when the water table drops below the well bottom, they go dry during times of drought.