An interlaboratory comparison was organised by JRC-IRMM among environmental radioactivity monitoring laboratories for the determination of gross alpha/beta activity concentration in drinking water. Independent standard methods were used for the reference value determination. The performance of participating laboratories was evaluated with respect to the reference values using relative deviations. Sample preparation and measurement methods used by the participating laboratories are detailed, in particular in the view of method-dependency of the results. Many of the participants’ results deviate by more than two orders of magnitude from the reference values regardless of the techniques used. This suggests that gross methods need revision.

JRC-Geel organised a Europe-wide proficiency test on gross alpha/beta activity concentration measurements in water with 154 participants from the field of environmental radioactivity monitoring. The performance of the participants was evaluated by comparing their results to the reference value using percentage deviation, z-score and zeta-score. Many of the participants' results deviated several orders of magnitude from the reference values regardless of the techniques used suggesting that the radioactivity monitoring of drinking water using gross-counting in Europe needs improving. Comparing with a similar proficiency test in 2012 reveals no major improvements and indicate that standards for gross-counting methods need revision. From the accompanied questionnaire, participants' measurement methods, laboratory practices and pitfalls were discussed. From the 14 best performing methods, JRC identified "Best practices".

Groundwater quality constantly evolves through rock–water interactions, which can enrich groundwater with undesirable elements such as naturally occurring radionuclides. The aim of this study was to understand the cause of gross alpha activity exceeding the screening value of 0.1 Bq L⁻¹ measured in groundwater-derived drinking water in the vicinity of a metamorphic outcrop in Hungary. As groundwater quality is strongly dependent on the properties of groundwater flow systems, environmental tracers (δ²H and δ¹⁸O composition, ²²⁶Ra, ²²²Rn, total U activity concentration, and ²³⁴U/²³⁸U ratio) and hydraulic evaluation were applied to understand groundwater dynamics. The collected groundwater samples had total U activities up to 540 mBq L⁻¹, which translates into an indicative dose below the drinking water parametric value. However, in the presence of dissolved uranium, the δ²H (−52.6–(−83.4)) and δ¹⁸O (−7.17–(−11.96)) values led to the conclusion that local flow systems were sampled that are known to be most vulnerable to any changes in their recharge area. The results confirm that the groundwater flow system approach involving environmental tracers and hydraulic evaluation is a powerful tool for identifying the cause of natural radioactivity in groundwater-derived drinking water.