The 1970s have produced both the wettest and the driest years in the U.S. since the 1930s, but despite the sharp contrasts of the past five years, on the average the nation's overall water supply has remained remarkably constant. This analysis by Walter Langbein, USGS National Center, Reston, Virginia, is based on a comparison of the charts of annual streamflow published by the USGS covering the past 57 water years. ‘The 1977 water year (October 1, 1976, to September 30, 1977) averaged 28% below normal and was actually one of the driest since 1954,’ Langbein said. ‘Only the 1931 and 1934 water years were drier, in terms of average streamflow.… In fact, 1973 averaged almost 40% above normal and was the wettest water year since at least 1927,’ he said. ‘This means that the nation's average streamflow dropped by roughly half, about 600 billion gallons per day, in the five years from 1973 to 1977’.