“The man on the farm over there says he pumps water directly from the ground and the supply is endless … he thinks there must a huge lake down there, at least that's what the old timers tell him.” This is a common notion about groundwater, one held by people around the world and one that we hope to dispel in this chapter. There is little doubt indeed that the ground holds immense amounts of water, but how does it get there and how and where is it stored? We will make a case for groundwater as a subsystem in the hydrologic cycle, an open system with inputs from and outputs to the surface water system that we discussed in the previous chapter. We also explore the geographic significance of groundwater and this leads us to the influences it has on the landscape, in particular on streams, lakes, wetlands, and land use. As we will discover, in a world that will see 3 billion additional people in the next 40 years, more than half of whom will be living in dry lands subject to the desiccating effects of global warming, groundwater's role in supplying water to cities, farms, and industry will reach levels of acuity unmatched in history.
Groundwater is Earth's single largest supply of fresh, liquid water. Humans have known about it and used it for thousands of years.The fi rst of ancient Rome’s aqueducts was fed by groundwater discharged from springs in the hills outside the city. The ancient qanats of the Middle East tapped into groundwater aquifers on mountain slopes, and tens of thousands of public wells have dotted the landscapes of China, India, and Europe since prehistoric times.