Water Wells -- Basic Components and Operation

A water well is an excavation or structure created in the ground by digging, driving, boring or drilling to access water in underground aquifers. The well water is drawn by an electric submersible pump, a vertical turbine pump, or a mechanical pump (eg from a water-pumping windmill). It can also be drawn up using containers, such as buckets, that are raised mechanically or by hand. Although not essential, a storage tank with a pressure of is usually added to the system (after the pump), so the pump does not need to operate constantly.To reduce the electricity required to pump up the water, often, a cistern is also added along with a small second pumpWells can vary greatly in depth, water volume and water quality. Well water typically contains more minerals in solution than surface water and may require treatment to soften the water by removing minerals such as arsenic, iron and manganese.

Drilled wells can get water from a much deeper level by mechanical drilling. Drilled wells with electric pumps are currently used throughout the world, typically in rural or sparsely populated areas, though many urban areas are supplied partly by municipal wells.

Drilled wells are typically created using either top-head rotary style, table rotary, or cable tool drilling machines, all of which use drilling stems that are turned to create a cutting action in the formation, hence the term 'drilling'. Most shallow well drilling machines are mounted on large trucks, trailers, or tracked vehicle carriages. Water wells typically range from 20 to 600 feet (180 m), but in some areas can go deeper than 3,000 feet (910 m).

Rotary drilling machines use a segmented steel drilling string, typically made up of 20-foot (6.1 m) sections of steel tubing that is threaded together, with a bit or other drilling device at the bottom end. Some rotary drilling machines are designed to install (by driving or drilling) a steel casing into the well in conjunction with the drilling of the actual bore hole. Air and/or water is used as a circulation fluid to displace cuttings and cool bits during the drilling. Another form of rotary style drilling, termed 'mud rotary', makes use of a specially made mud, or drilling fluid, which is constantly being altered during the drill so that it can consistently create enough hydraulic pressure to hold the side walls of the bore hole open, regardless of the presence of a casing in the well. Typically, boreholes drilled into solid rock are not cased until after the drilling process is completed, regardless of the machinery used.

Drilled wells are usually cased with a factory-made pipe, typically steel (in air rotary or cable tool drilling) or plastic/PVC (in mud rotary wells, also present in wells drilled into solid rock). The casing is constructed by welding, either chemically or thermodynamically, segments of casing together. If the casing is installed during the drilling, most drills will drive the casing into the ground as the bore hole advances, while some newer machines will actually allow for the casing to be rotated and drilled into the formation in a similar manner as the bit advancing just below. PVC or plastic is typically welded and then lowered into the drilled well, vertically stacked with their ends nested and either glued or splined together. The sections of casing are usually 20' (6 m) or more in length, and 6"–12" (15 to 30 cm) in diameter, depending on the intended use of the well and local groundwater conditions.