The perceived flavor of coffee varies depending on the composition of the brewing water, and the influencing mechanisms are poorly understood. To investigate the effect of dissolved divalent cations on the extraction of organic acids in coffee, magnesium and calcium chloride salts were added pre- and post-brew. Citric, malic, lactic and quinic acid were analyzed using gas chromatography – mass spectrometry and nuclear magnetic resonance techniques. At concentrations typically found in drinking water, the salts resulted in limited variation of the acid content, while ten-fold higher salt concentrations produced more pronounced variations. Comparisons between pre- and post-brew additions showed similar acid content in most cases, suggesting that extraction of acids proceeds independent of the water composition. Interactions taking place post-brew may, however, influence the perceived flavor. A scientific basis for water quality recommendations in the coffee industry is long overdue and this work provides experimental and analytical contributions to continued research.