Skip to main content Skip to main content

The Habitable Planet: A Systems Approach to Environmental Science 

Water Resources

Earth's water resources, including rivers, lakes, oceans, and underground aquifers, are under stress in many regions. Humans need water for drinking, sanitation, agriculture, and industry; and contaminated water can spread illnesses and disease vectors, so clean water is both an environmental and a public health issue. In this unit, learn how water is distributed around the globe; how it cycles among the oceans, atmosphere, and land; and how human activities are affecting our finite supply of usable water.


Unit 8: Water Resources // Glossary

Underground formations, usually composed of sand, gravel, or permeable rock, capable of storing and yielding significant quantities of water.

Describes a confined aquifer containing groundwater that will flow upwards out of a well without the need for pumping.

catchment area
The area that draws surface runoff from precipitation into a stream or urban storm drain system.

Defined by the Clean Water Act as the addition of pollutants (including animal manure or contaminated waters) to navigable waters.

Coastal waters where seawater is measurably diluted with freshwater; a marine ecosystem where freshwater enters the ocean.

Water without significant amounts of dissolved sodium chloride (salt). Characteristic of rain, rivers, ponds, and most lakes.

Water contained in porous strata below the surface of the Earth.

hydraulic head
The force per unit area exerted by a column of liquid at a height above a depth (and pressure) of interest. Fluids flow down a hydraulic gradient, from points of higher to lower hydraulic head.

Referring to a condition in which natural waters have a low concentration of dissolved oxygen (about 2 milligrams per liter, compared with a normal level of 5 to 10 milligrams per liter). Most game and commercial species of fish avoid waters that are hypoxic.

nonpoint source
A diffuse, unconfined discharge of water from the land to a receiving body of water. When this water contains materials that can potentially damage the receiving stream, the runoff is considered to be a source of pollutants.

non-aqueous phased liquids (NAPL)
Organic liquids that are relatively insoluble in water and less dense than water. When mixed with water or when an aquifer is contaminated with this class of pollutant (frequently hydrocarbon in nature), these substances tend to float on the surface of the water.

The ease with which water and other fluids migrate through geological strata or landfill liners.

point source
An identifiable and confined discharge point for one or more water pollutants, such as a pipe, channel, vessel, or ditch.

The total volume of soil, rock, or other material that is occupied by pore spaces. A high porosity does not equate to a high permeability because the pore spaces may be poorly interconnected.

A hydrologic process where water moves downward from surface water to groundwater. This process usually occurs in the vadose zone below plant roots, and is often expressed as a flux to the water table surface.

The physical or chemical linkage of substances, either by absorption or by adsorption.

total maximum daily load
The maximal quantity of a particular water pollutant that can be discharged into a water body without violating a water quality standard.

vadose zone
The area of the ground below the surface and above the region occupied by groundwater.

The area of land that drains into a lake or stream.

Series Directory

The Habitable Planet: A Systems Approach to Environmental Science 


Harvard Smithsonian Center for Astrophysics in association with the Harvard University Center for the Environment. 2007.
  • Closed Captioning
  • ISBN: 1-57680-883-1