Determination of such fundamental hydrologic factors as the coefficients of permeability, transmissibility, and storage; areas of recharge and discharge; direction of ground-water movement; the safe yield; and other pertinent, related factors are based in part upon water-level measurements in wells. But these water-level readings, if not properly understood or weighted, may be entirely misleading. This is because water levels are neither stationary nor steadily rising (with recharge) or falling (with discharge). Water levels fluctuate as a result of several factors other than those of changes in recharge or discharge, chief among which are: (1) tides; (2) atmospheric pressure; (3) winds; (4) earthquakes; and (5) passing trains. Characteristically, artesian aquifers respond to these forces in a manner different from that of nonartesian aquifers, but in some places local geologic conditions in a nonartesian aquifer may cause water-level fluctuations ordinarily found only in artesian wells. Among the unusual features observed is a 4.5-foot fluctuation of water level in a Miami well caused by earthquake waves originating 750 miles away in the Atlantic Ocean, off the coast of the Dominican Republic. Quakes from all over the world are responsible for water-level fluctuations in this and other wells in the Miami area.