There are two accepted doctrines governing rights to percolating waters: (1) absolute ownership; (2) reasonable use. At present, the only generally accepted legal principle concerning the use of percolating water is that any reasonable, legitimate use of one's land which interferes with the flow of percolating waters to another's land produces no liability. Virginia purports to follow the 'common enemy' doctrine which permits each landowner to fight off surface water as best as he can. The legal principles applicable to underground watercourses are almost identical to those which apply to surface watercourses. The primary difference concerns the requirements for establishing the existence and location of an underground watercourse. (Author)