Another method is called spray irrigation where water is sprayed or dripped on the crops. Ground water , which is in aquifers below the surface of the Earth, is among the Nation's most important natural resources. Even some major cities, such as San Antonio, Texas, rely solely on ground water for all their needs. Withdrawals of ground water are expected to rise in the coming century as the population increases and available sites for surface reservoirs become more limited. Question List 6.
Ground water is water occurring in the zone of saturation in an aquifer or soil.
Other than the location, one of the primary differences between surface and ground water is that ground water moves much slower than surface water. This is because ground water experiences far more friction as it moves through the pores in soil then surface water experiences as it flows over the earth's surface. Surface water is much more easily contaminanted than ground water. Filtration through the soil helps clean ground water. Question List 7.