Lake Velence is a shallow soda lake whose water level and water quality show a severely deteriorating tendency in recent years. Until recently, the groundwater component in the lake’s water budget has not been taken into consideration. To integrate the lake into the groundwater flow system at the regional scale, methods of “basin hydraulics” were applied. In addition, 17 water samples were collected for δ²H and δ¹⁸O, and for ΣU, ²²⁶Ra and ²²²Rn activity measurements to use these parameters as environmental tracers of groundwater contribution. Groundwater mapping revealed that groundwater recharges in Velence Hills and the local elevations south of the lake, whereas discharge occurs by the lake’s shoreline and along surface watercourses. The results indicated that Lake Velence is the discharge point of local groundwater flow systems known to be more sensitive to climate changes and anthropogenic activities (e.g., contamination, overexploitation). Groundwater and lake water have similar uranium activity concentrations serving as another sign of groundwater inflow into the lake. Therefore, it is necessary to consider both the groundwater component in the lake’s water management and its vulnerability regarding local and short-term changes in the catchment area.

Since 2017 Switzerland has new regulations concerning natural radionuclides in drinking water. They are very close to the ones in force in the EU (213/51/EURATOM). Clear limits for relevant natural radionucdlides have been replaced by rather vague “parametric values” and an “indicative dose”. This has lead to a general confusion at the Federal and the Cantonal environmental radioactivity labs about how to enforce the new regulations. What has to be monitored, how often and by what analytical methods ? Do we have enough data about the situation in Switzerland ? Do we need a large screening or are there criteria for a targeted search ?To answer these questions all available data have been pooled. Data left after a critical review have been used for frequency distributions and maps.It has turned out that natural radionuclides are not a general problem in Swiss drinking water. Hot spots are concentrated in some regions and can well be explained by the local geology.Thus there is no need for a “blind” screening. A targeted search, based on the geology is all we need.Concerning the analytical methods, Total-Alpha and Total-Beta measurements are out of date since many decades. They are also unreliable and give wrong results about the Ra-228 contribution to the ingested dose. Only nuclide specific analytical method are recommended.Other recommendations are that bottled waters should be considered drinking water, complying with the same limits and that ingestion doses from radon should not be neglected.