Uranium is a long-lived radionuclide typically present at the g/g g/g g/g g/g level in rocks and soils, and at the g/Lg/Lg/L level in natural waters. Uranium has three isotopes (234U, 235U and 238U), all of which decay by alpha and gamma emissions. Dissolved uranium in groundwater is a potential threat for human health (due to its chemical nephrotoxicity and radioactivity (WHO, 2005). In the Irish context, elevated uranium concentrations were documented in some private wells in the past (EPA, 2003), leading to concerns about the quality of the groundwater in some rural areas. High concentrations of U occur in granites (enriched by up to two orders of magnitude over oceanic basalts), in clastic sediments such as sandstones, greywackes and shales (0.5 – 4 ppm) and in organic-rich “black” shales (3-1,200 ppm), metamorphic rocks and marine phosphates. Guided by geological and the recently released Tellus stream sediment data, new preliminary data for groundwaters samples from SE Ireland show elevated uranium concentrations in some private wells, particularly in the vicinity of Baltinglass, Co. Wicklow, and Hacketstown/Borris, Co. Carlow. Results from Hacketstown indicate a link between dissolved U concentrations and groundwater carbonate alkalinity, indicating a solubility control by the carbonyl ion (CO32-), likely linked to the occurrence of secondary calcite in the Tullow Pluton of the Leinster Granite. In the granite-derived fracture-controlled groundwater samples, a strong correlation was found between electrical conductivity and U concentrations, implying that simple field-based conductivity measurements can be used to identify samples with elevated uranium contents in these waters. Finally, the nature of uranium sources (primary or secondary remobilised) is being evaluated by measuring the 234U/238U activity ratio of the dissolved uranium. Sources linked to primary igneous minerals are likely to have high 234U/238U ratios, close to secular equilibrium, whereas previously weathered secondary sources are likely to be characterised by lower 234U/238U ratios, reflecting previous preferential loss of 234U during weathering.