A water well is an artificial excavation or structure put own by any method such as digging, driving, boring, or drilling for the purposes of withdrawing water from underground aquifers. Well water may be drawn via a electric submersible pump or a mechanical pump (eg from a water-pumping windmill), from a source below the surface of the earth. Alternatively, it could be drawn up using containers, such as buckets, that are raised mechanically, or by hand. Although not essential, usually a storage tank with a pressure of 40-60 psi is also added to the system (after the pump), so the pump does not need to operate constantly.