• Groundwater
    WHOI researcher Ann Mulligan collect data about groundwater discharge into Waquoit Bay, Mass. (Photo by Tom Kleindinst, Woods Hole Oceanographic Institution)

Groundwater is water that exists underground in the spaces between grains of sand or gravel or in the cracks and fractures in solid rock.

More than 50 percent of the people in the United States, including almost everyone who lives in rural areas, use ground water for drinking and other household uses. Ground water is also used in some way by about 75 percent of cities and by many factories. The largest use of ground water is to irrigate crops. 

Groundwater is also an important part of the global water cycle, and a sizeable portion of it eventually finds its way to the ocean. On its way, groundwater dissolves minerals, nutrients, and pollutants, carrying them along for the ride. Scientists study groundwater to understand the composition of materials underground and the nature of chemical reactions that occur there.