Hydrogeology

thumb|upright=1.5|The Earth captured in the [[Pacific Ocean side]]

thumb|upright=1.8|Schematic of an aquifer showing confined zones, groundwater travel times, a spring and a [[well]]

[[File:Boy drinks from a tap at a NEWAH WASH water project in Puware Shikhar, Udayapur District, Nepal. (10677903803).jpg|thumb|270x270px| Boy drinks from a tap at a NEWAH WASH water project in Puware Shikhar, Udayapur District, Nepal.]

Porosity or void fraction is a measure of the void (i.e. "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Strictly speaking, some tests measure the "accessible void", the total amount of void space accessible from the surface (cf. closed-cell foam).

area in an aquifer, below the water table

spring that is part of a karst system

top of a saturated aquifer, or where the water pressure head is equal to the atmospheric pressure

the unsaturated aquifer above the water table

movement of saline water into freshwater aquifers

unit of permeability

subsurface layer in which groundwater seeps up from a water table by capillary action

layer of fresh groundwater

insects seeking out nutrients in certain moist substances such as rotting plant matter

thumb|upright=1.35|A seep puddle in a [[forest clearing]] A seep or flush is a moist or wet place where water, usually groundwater, reaches the Earth's surface from an underground aquifer.

type of waterbody

water that collects in a mine and which has to be brought to the surface by water management methods

drainage of agricultural lands by wells

thumb|upright=1.5|View from the International Space Station of [[Lake Lucero in the Tularosa Basin, an example of a bolson.]] A bolson is a desert valley or depression, usually draining into a playa or salt pan, and entirely surrounded by recently uplifted hills or mountains. Bolsons are sites of active deposition of sediments (aggradation). They are a type of endorheic basin characteristic of basin and range topography.

type of scientific model

alteration of a surrounding environment by the presence of a water source

insoluble groundwater contaminant denser than water