The following paper outlines the general characteristics of surface waters in Minnesota and the various factors that tend to modify the quality of the drainage. It includes the results of nearly two years' field and laboratory work done by the United States Geological Survey in cooperation with the Minnesota State board of health. First the general features, both natural and economic, that influence the quality of the meteoric water and impart to the lakes and streams their essential characteristics are reviewed. Next each drainage area is considered in detail, the streams are described, the sources of pollution are discussed, and the results of chemical analyses and bacteriological examinations are given. Statistics are presented regarding practically all of the municipal water supplies in the State, and the relative value of the surface and ground waters for general consumption is discussed. At the end is a description of the laboratory methods employed in the chemical and bacteriological work. During the summer of 1903 arrangements were made whereby a study of Minnesota surface waters was commenced jointly by the United States Geological Survey, the Minnesota State board of health, and the chemical department of the University of Minnesota. Certain sections of the State were assigned to each party of the agreement for investigation. In pursuance of this project samples were collected at Brainerd, Hastings, Mankato, Prescott, Rochester, St. Cloud, Sank Rapids, and Wabasha, during the fall of 1903, by representatives of the Minnesota State board of health. Three trips over the territory assigned to the United States Geological Survey were made by R. B. Dole, assistant hydrographer, between November 25, 1903, and May 22, 1904, during which time samples were collected at Aitkin, Bemidji, Biwabik, Brainerd, Cass Lake, Cloquet, Crookston, Ely, Eveleth, Grand Rapids, Hibbing, Sparta, Tower, and Virginia. During the first seven months of 1904 samples were collected by representatives of the State board of health at Anoka, Fort Snelling, Granite Falls, Hastings, Mankato, Montevideo, New Ulm, Ortonville, Prescott, Redwood Falls, Rochester, and Wabasha. (PI. I.) At each place visited samples were collected in glass bottles and forwarded to express for chemical analysis to the State laboratories, where they were examined by H. C. Carel, assistant professor in medical chemistry. University of Minnesota, who was employed by the State board of health to perform the chemical examinations of water. Samples for bacteriological examination were also collected at the same time and plated in the field and the cultures were sent by express to the laboratory for incubation and examination. In addition, field tests were made for certain constituents at the time of collection. In the summer of 1904 an agreement between the United States Geological Survey and the State board of health was made, by which an employee of the Survey was detailed by the Survey and appointed by the board to do such chemical work from August 1, 1904, to July 31, 1905, inclusive, as might be necessary in an extended examination of waters of the lakes and streams of Minnesota. During that period the chemical analyses were performed by R. B. Dole, assistant hydrographer, in a laboratory at Minneapolis specially equipped for the purpose by the State board of health. The bacteriological examination of the water samples was conducted as formerly in the laboratory of the State board of health, by Dr. E. H. Beckman, assistant bacteriologist to the board. Both the chemical and the bacteriological work were, during the entire cooperation, under the immediate supervision of Dr. F. F. Wesbrook, director of the laboratories of the State board of health of Minnesota. In order to continue the comprehensive survey of the surface waters in the State, points were selected in each drainage area at which samples should be taken at regular intervals for examination. Sixty-five stations were thus established, at which samples were taken in regular series one sample during the fall of 1904. one during the winter of 1904-5, and one during the spring of 1905. In addition to the results obtained by the laboratory work thus performed, it was considered especially important to procure all available information concerning matters of hydro-economic importance in the sections visited, and a large amount of time was expended in gathering data concerning every feature of municipal activity which in any way affects water in its relation to public health or public utilities. At every place where it was possible, a personal inspection was made of waterworks systems, sewerage, and effluent-discharging factories, and detailed information was obtained concerning water and sewerage systems, ice supply, sewage-disposal works, water-borne diseases, and general water resources. In this manner information was procured regarding a majority of the principal cities and villages. In the spring of 1905 correspondence was carried on with reliable persons in such important settlements as had not been visited in order to procure the same kind of information, so that by the end of July, 1905, data were on file concerning practically every settlement in the State having a population of more than 1,000 according to the census of 1900, and also concerning practically every waterworks system in the State. Active field work was discontinued on June 30, 1905. For many courtesies extended and for information given, acknowledgments are here made to the health officers, waterworks superintendents, city clerks, and others who collaborated with the authors in this investigation. Special thanks are due to Dr. H. M. Bracken, secretary of the State board of health, for his enthusiastic support and for his vast local and general knowledge of the State, which was at all times made available by him in the work; thanks are also due to the individual members of the State board of health, who supported the work heartily throughout and by their interest made it possible, and to the individual members of the staff of the laboratories of the State board of health, who rendered every assistance whenever it was desired. Mr. Marshall O. Leighton, chief hydrographer, water resources branch U. S. Geological Survej", originally suggested the work and has followed it carefully throughout, guiding it and helping in the correlation of the practical and scientific sides at all times.