Open access nationwide data sets for drinking water hardness at public waterworks and their water supply areas in Denmark

Three spatiotemporal data sets of drinking water hardness in Denmark (version 1) are presented here: (1) annual drinking water hardness at public waterworks (1905–2023); (2) annual drinking water hardness at their water supply areas (1978–2023) and (3) the latest drinking water hardness at the water supply areas (1980–2023). Raw data were extracted from the Jupiter database for groundwater and drinking water data in Denmark, and were quality-assured. Hardness was calculated after semi-automatic outlier exclusion based on Ca and Mg, or if not available, the reported total hardness. Data were further aggregated at the waterworks level by the annual mean and at the supply area level by the weighted mean (weighted to waterworks annual abstraction volumes). Temporal and spatial gaps were filled prior to these aggregations. Various stakeholders could benefit from these open access data. They provide a societal service in response to increased public interest in drinking water hardness. The research community could use the data in environmental, exposure or epidemiological assessments. Finally, the water supplies and the public sector could benefit from these data as they provide a nationwide overview of current and past drinking water hardness in Denmark and highlight the geographic areas that lack recent data, most probably due to de-regulation.