i'm tom maddock. i'm at the university of arizona, and i study hydrology. i work in the area of ground-water/surface-water interactions. basically, the difference between ground water and surface water is you can float a stick in surface water. in ground water, you really can't do that except maybe looking down a well and dropping the stick down the well. narrator: surface water is typically found lakes, rivers, and streams. ground water is found beneath the earth's surface in small pores and fractures found within large rock formations. when this water is readily available for human use, these formations are called aquifers. almost all of the natural surface water in arizona has been developed leaving only ground water available for human consumption. dr. maddock: the problem in the southwest is that we basically are having continued growth, and, in many places, the only place that you can get water to sustain that growth is from ground-water development. unfortunately, ground water is more available near the streams than it is other places. it's what we c