Water resources data for the 1978 water year for Arizona consist of records of stage, discharge, and water quality of streams; stage, contents, and water quality of lakes and reservoirs; water levels of observation wells; and quality of ground water. This report contains discharge records for 241 gaging stations, annual peaks for 77 crest-stage partial-record stations, and discharge measurements at 58 miscellaneous sites; contents only records for 9 lakes and reservoirs; stage and contents for 1 lake; elevations only for 2 lakes or reservoirs; gage height only for 1 lake and 1 head over a dam; 16 supplementary records, included with gaging-station records, consisting of month end or monthly stage, contents, and evaporation of lakes and reservoirs, diversions, and return flows; 2 low-flow investigations; water-quality records for 87 continuous record stations and 16 miscellaneous sites; water levels for 101 observation wells; and water-quality data for water from 189 wells. The data represent that part of the National Water Data System operated by the U.S. Geological Survey and cooperating Federal and State Agencies in Arizona.