This chapter shows long-term data and trends in precipitation and surface water chemistry for each site.  It contains a brief introduction to the topic, and methods of measurements, selection of variables, and their data source. It consists primarily of a large number of figures showing long-term data for different variables.  Volume-weighted concentration (mg/L) and area-based wet deposition (kg/ha) from precipitation, and concentration in surface water (mg/L) of nitrogen (as nitrate and ammonium), sulfur (as sulfate), chloride, and calcium are selected.  Two types of graphs are included to show trends in the variables and to provide a sense of change across a range of spatial scales (continent, site) for each variable: maps at continental scale showing either the mean across years or the slope of the regression line (if significant) across time, and site-scale data through time.  Nitrate and sulfate deposition are decreasing in many Eastern sites, consistent with efforts to control emissions of acid-causing nitrogen and sulfur from power plants in this part of the country.