There are certain localities in which the under layers of the soil consist largely of sand, through which water percolates with more or less facility. The water which may be secured in such localities by digging into the sand may be regarded as a supply from Nature's sand filtration plant. The most economical method of securing a water supply from such sources is by means of a driven well. A "driven well" is an ordinary iron pipe driven into the surface by means of being attached to a steel point, and as each section of pipe is added to that which has gone below the whole tube is forced deeper into the soil until it finally penetrates the water-bearing sand layers. The first section of pipe which is driven into the soil is furnished with finely perforated sides through which the water can enter and all the particles of sand be excluded. The water usually rises to near the surface of the earth and is removed by ordinary pumping. Hundreds of wells of this kind can be put down under favorable circumstances and be kept supplied to their full capacity by the natural seepage of the water through the sand layers. The quantity of water which can be secured in this way is of course limited to the area and character of the water-bearing sand. This method of supply is usually resorted to only for very small cities. A very good quality of water is usually secured by this method, due to the complete filtration to which it is subjected in the ground.