In hydrologic terms, a “gaining stream” is a surface stream augmented by groundwater flow. In a more conventional sense of the term, legal and policy disputes surrounding groundwater are also “gaining” in importance, though localized groundwater-related issues have perplexed the courts for generations. In a 1903 opinion, at the end of a lengthy discourse summarizing various authorities on the subject of groundwater withdrawals, Justice John B. Winslow of the Wisconsin Supreme Court admitted that “[p]erhaps more time has been spent in reviewing these decisions than is profitable, but the subject is interesting, and . . . should be given serious consideration.”[1] Winslow’s comments came during the latter part of a long period of judicial unfamiliarity with the science of groundwater. Nineteenth century jurists characterized its movement and sometimes its very existence as “unknown”[2] or even “occult.”[3]

About two-thirds of Wisconsinites draw their drinking water from the ground. Still, both in this state and elsewhere, groundwater lacks the intuitive familiarity of surface water. Perhaps as a result, many states still don’t have well-developed jurisprudence or legal management systems for groundwater even though hydrogeology has become a well-developed and well-accepted science. Judicially-created groundwater doctrines vary widely from state to state. This legal dissonance is of increasing concern in light of a surge of groundwater problems and disputes involving water quality concerns, the viability of the public trust doctrine as a tool for groundwater regulation, and transboundary management issues, among many others. This societal and legal evolution proves Justice Winslow correct: The law of groundwater is indeed “interesting,” and courts are giving it ever more “serious consideration.” Consider the following examples: