aquifers
	Porous, water-bearing layers of sand, gravel, and rock below the earth's surface; reservoirs for groundwater.
artesian
	The result of a pressurized aquifer intersecting the surface or being penetrated by a pipe or conduit, from which water gushes without being pumped; also called a spring.
condensation
	The aggregation of water molecules from vapor to liquid or solid when the saturation concentration is exceeded.
condensation nuclei
	Tiny particles that float in the air and facilitate the condensation process.
consumption
	The fraction of withdrawn water that is lost in transmission or that is evaporated, absorbed, chemically transformed, or otherwise made unavailable for other purposes as a result of human use.
degradation (of water resource)
	Deterioration in water quality due to contamination or pollution; makes water unsuitable for other desirable purposes.
desalination
	Removal of salt from water by distillation, freezing, or ultrafiltration.
dew point
	The temperature at which condensation occurs for a given concentration of water vapor in the air.
discharge
	The amount of water that passes a fixed point in a given amount of time; usually expressed as liters or cubic feet of water per second.
evaporation
	The process in which a liquid is changed to vapor (gas phase).
groundwater
	Water held in gravel deposits or porous rock below the earth's surface; does not include water or crystallization held by chemical bonds in rocks or moisture in upper soil layers.
infiltration
	The process of water percolation into the soil and pores and hollows of permeable rocks.
rain shadow
	Dry area on the downwind side of a mountain.
recharge zone
	Area where water infiltrates into an aquifer.
relative humidity
	At any given temperature, a comparison of the actual water content of the air with the amount of water that could be held at saturation.
residence time
	The length of time a component, such as an individual water molecule, spends in a particular compartment or location before it moves on through a particular process or cycle.
runoff
	The excess of precipitation over evaporation; the main source of surface water and, in broad terms, the water available for human use.
saltwater intrusion
	Movement of saltwater into freshwater aquifers in coastal areas where groundwater is withdrawn faster than it is replenished.
saturation point
	The maximum concentration of water vapor the air can hold at a given temperature.
sinkholes
	A large surface crater caused by the collapse of an underground channel or cavern; often triggered by groundwater withdrawal.
stable runoff
	The fraction of water available year round; usually more important than total runoff when determining human uses.
sublimation
	The process by which water can move between solid and gaseous states without ever becoming liquid.
subsidence
	A settling of the ground surface caused by the collapse of porous formations that result from withdrawal of large amounts of groundwater, oil, or other underground materials.
water table
	The top layer of the zone of saturation; undulates according to the surface topography and subsurface structure.
withdrawal
	A description of the total amount of water taken from a lake, river, or aquifer.
zone of aeration
	Upper soil layers that hold both air and water.
zone of saturation
	Lower soil layers where all spaces are filled with water.

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