Water resources data for the 2003 water year for Pennsylvania consist of records of discharge and water quality of streams; contents and elevations of lakes and reservoirs; and water levels and water quality of ground-water wells. This report, Volume 1 contains (1) discharge records for 79 continuous-record streamflow-gaging stations, 8 partialrecord stations, 19 special-study and miscellaneous streamflow sites; (2) elevation and contents records for 13 lakes and reservoirs, and water-quality records for 6 lakes and reservoirs; (3) water-quality records for 37 gaging stations and 12 ungaged streamsites; (4) water-quality records for 67 special-study stations; (5) water-level records for 49 network observation wells; and (6) water-quality analyses of ground water from 10 ground-water wells. Site locations are shown in figures 6-13. Additional water data collected at various sites not involved in the systematic datacollection program are also presented. These data together with the data in Volumes 2 and 3, represent that part of the National Water Data System operated by the U.S. Geological Survey and cooperating State, local, and Federal agencies in Pennsylvania. *Pennsylvania, *Hydrologic data, *Ground water, *Surface water, *Water quality, Gaging stations, Streamflow, Flow rates, Lakes, Reservoirs, Chemical analysis, Sediments, Water temperature, Water resources data for the 2003 water year for Pennsylvania consist of records of discharge and water quality of streams; contents and elevations of lakes and reservoirs; and water levels and water quality of ground-water wells. This report, Volume 1 contains (1) discharge records for 79 continuous-record streamflow-gaging stations, 8 partialrecord stations, 19 special-study and miscellaneous streamflow sites; (2) elevation and contents records for 13 lakes and reservoirs, and water-quality records for 6 lakes and reservoirs; (3) water-quality records for 37 gaging stations and 12 ungaged streamsites; (4) water-quality