Drawdown - the vertical drop of the water level in a well caused by ground water pumping; also, the difference between the water level before pumping and the water level during pumping.

Ground water – water found in the saturated zone of the subsurface.

Ground water aquifer – a water-bearing layer of rock or sediment capable of yielding usable quantities of water; composed of unconsolidated materials such as sands and gravel, or consolidated rock such as sandstone or fractured limestone.

Overwithdrawal - withdrawal of ground water from an aquifer at a rate that exceeds the recharge rate of that aquifer. Can lead to lowered water table, saltwater intrusion and sinkholes.

Permeability - the capacity of a porous rock, sediment, or soil to transmit ground water. It is a measure of the inter-connectedness of a material's pore spaces and the relative ease of fluid flow under unequal pressure.

Pores – the spaces between particles within geological material (rock or sediment) occupied by water or air.

Porosity - is defined as the ratio of the volume of voids to the volume of aquifer material. It refers to the degree to which the aquifer material possesses pores or cavities which contain air or water.

Recharge area or zone - Recharge is the process that allows water to replenish an aquifer. This process occurs naturally when rainfall filters down through the soil or rock into an aquifer. Artificial recharge is achieved through the pumping (called injection) of water into wells or by spreading water over the surface where it can seep into the ground. The land area where recharge occurs is called the recharge area or recharge zone

Salt water intrusion - the process by which over-pumping from an aquifer creates a flow imbalance within an area, which results in salt water encroaching into and contaminating a freshwater supply.

Saturated zone - the subsurface zone in which all pores in the aquifer are filled with water.

Spring – a place where ground water naturally comes to the surface at the intersection of the water table and land surface.

Subsidence –the sinking or depression of the land surface as a result of too much ground water withdrawal (or overwithdrawal of any mined fluid such as petroleum).

Surface water - water found on the land surface in streams, ponds, marshes, lakes or other water bodies.

Unconsolidated material - material derived from the disintegration and erosion of consolidated rocks on the land's surface, as well as sediments deposited by coastal and glacial processes. Unconsolidated materials include, in order of increasing grain size, clay, silt, sand, and gravel.

Underground water - all water beneath the land surface. It includes water in the saturated and unsaturated zones.

Unsaturated zone - the subsurface zone in which the geological material contains both water and air in pore spaces. The top of the unsaturated zone typically is at the land surface, otherwise known as the vadose zone.

Watershed – all the land area and water within the confines of a drainage divide in which all surface runoff will pass through an identifiable outlet, such as a stream or river.

Water table -the top of an unconfined aquifer below which the pore spaces are generally saturated; the level in the saturated zone at which the pressure is equal to the atmospheric pressure.

Water table well – a well in which the source of water is an unconfined water table aquifer.