Inorganic chemical quality of European tap-water: 1. Distribution of parameters and regulatory compliance

•A pan-European survey comprises >60 inorganic parameters in 579 tap water samples.•Compliance with standards for inorganic parameters is good (>99% in EU states).•Around 1% non-compliance is observed for arsenic and 0.2% for uranium.•No sample of water contained nitrate in excess of 45 mg/L.•A weak co-variation in Cu and Pb could indicate derivation from plumbing.

579 tap water samples were collected at the European scale and analysed in a single laboratory for more than 60 parameters. This dataset is evaluated here in terms of the statistical distribution of the analysed parameters and compliance with EU and international drinking water regulations. For most parameters a 99% (or better) degree of compliance was achieved. Among the parameters with the higher rates of non-compliance are: arsenic (1% non-compliance in EU member states, 1.6% when samples from non-EU states are also considered) and sodium (0.6%/1.0%). The decision by the WHO to raise its provisional guideline from 15 μg/L (WHO, 2004) to 30 μg/L (WHO, 2011) has reduced non-compliance for uranium from 1.0% to 0.2%. Despite the fact that tap water (i.e. presumed treated water) was collected, many observations can still be interpreted in terms of hydrogeochemical processes. The dataset demonstrates the potential value of very cost-effective, low-density sampling approaches at a continental (European) scale.