Ground water, a plentiful and largely underdeveloped resource of Wisconsin, has good to excellent chemical quality in most places. This resource is readily available in most parts of the State for municipal, industrial, and rural uses. In 1970, about 0.5 billion gallons of ground water a day was pumped in Wisconsin for all uses (Murray and Reeves, 1972). In addition, underground reservoirs discharge an average of 16 billion gallons per day of water of relatively constant temperature and uniform quality, which maintains the base flow of streams and the level of lakes (Holt, 1964).