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High As groundwater has been widely found in inland basins of P.R. China, which has posed a serious health risk to the local residents. Although these inland basins experience the same arid to semiarid climate and are filled with Quaternary sediments, As concentrations show big variations. Three inlands basins have been investigated to characterize hydraulic conductivities and geochemistry of the groundwater and sediments, and evaluate their controls on dissolved As concentrations. Dissolved As concentrations ranged between < 0.1 and 105 mu g/L (average 27.8 mu g/L), between < 0.1 and 338 mu g/L (average 94.0 mu g/L), and between 0.33 and 857 mu g/L (average 130 mu g/L) in the Yinchuan basin (YC), the Songnen basin (SN), and the Hetao basin (HT), respectively. In the YC, although Fe and Mn concentrations are the highest, groundwater has the lowest As concentration. lonically bound As fraction and strongly adsorbed As fraction of sediments are the highest in the HT and the lowest in the YC basin. Groundwater As is predominantly regulated by these mobilizable As forms in sediments. However, the predominant factors controlling groundwater As are dependent on the scale of the study area. At the average multi basin scale, groundwater flushing evidently decreases groundwater As concentrations. At the individual scale of the sampling site, due to the similar groundwater flow rate, redox conditions are the key factor controlling groundwater As, with more As partitioned into groundwater of lower Eh values. Variations in these factors controlling groundwater As suggest that safe wells can be expected in the basins with high groundwater flow rates and at sites with higher groundwater Eh values. (C) 2016 Elsevier Ltd. All rights reserved.