Objectives: In order to explore the spatial—temporal variations of groundwater hydrochemical characteristics and their potential controlling factors in the small coastal watershed, based on an adequate volume of hydrochemical data, the Dagu River Basin in Qingdao was taken as the research object in this paper.Methods: Groundwater hydrochemistry datasets used in this study, collected from 18 sampling sites of the Dagu River Basin, spanning 2001 to 2012, were composed of eight major ions (Cl-, SO2-4, HCO-3, NO-3, Na+, K+, Mg2+ and Ca2+), pH and total dissolved solids (TDS). Statistical analyses were applied to explain the spatial and temporal variations of the major hydrochemical constituents, and correlation analysis was undertaken to examine the relationship between the considered variables. The Piper plot (1944), Gibbs diagram (1970) and major ratio bivariate plots were used to identify the evolution of the groundwater hydrochemical characterizations in the Dagu River Basin.