Water composition in the unsaturated zone was sampled at Sete Cidades caldera, located in São Miguel (Azores archipelago), in order to study the impact of agriculture in water quality. Data from two field sites are discussed, one of which corresponds to a pasture land, where agriculture is taken place (Pa I), while in the other (village), human activity is limited. In the village site waters present low mineralization and are from the Cl-Na type. In the Pa I waters present a higher mineralization, and defines a trend line, from the more superficial suction cup to the deeper, representing an evolution toward a relative composition similar to the perched-water bodies. This trend is revealed by a shift from a Mg-Ca cationic composition to Na-dominated waters. Comparing NO3 contents from both sites is possible to show a sharp difference, as values are higher where agriculture is developed.