A suite of shallow and deep subsurface waters from southwestern Illinois has been analyzed for chlorine (CT), bromine (Br–), and sodium (Na+) using three different methods. Cl and Br were analyzed by ion chromatography (IC) and neutron activation analysis (NAA). Na was analyzed using inductively coupled plasma-atomic emission spectrometry (ICP-AESS) and NAA. In addition, five water standards were prepared with compositions over the range of Cl, Br, and Na concentrations in the natural waters were analyzed using the same methods. Analytical results for the prepared standards by the different methods were in good agreement. However, analytical results on natural waters yielded generally poor agreement between the methods. Our results suggest that solute concentrations and ratios between major solutes in subsurface waters determined by IC and ICP-AES may involve substantial laboratory error.