Elements in Tap Water - Part 2 - Quality Assurance of Analysis

Abstract

Due to the inclusion of the quality of the water distribution system in the DWD this new directive prescribes new parametric values and the performance characteristics. The trueness, precision and limit of detection are defined as percentage of the parametric value. In the framework of our research on the effect of products on the quality of drinking water at the consumers¿ tap, we studied the quality of our data using certified reference water and four selected samples. Elements additional to the DWD, i.e. those evaluated by the WHO and those mentioned in national regulations concerning the acceptance of products that come in contact with drinking water, were included in our study. Analysis of the certified standard revealed that K, Pb and Se might only suffer from a small systematic error whereas As and Ca might suffer a bigger systematic error (P=0.05). The trueness of As is out of range compared to what is defined in the DWD. The trueness of Cu and Pb is at the edge. The precision of As and Se are on the edge. In general, the low concentrations in the samples compared to the parametric values in the DWD result in slightly or significantly lower precisions. The precision of Al, Ca, Fe, Mg and Zn for the samples is lower compared to that of the certified standard at a similar concentration level whereas U showed the opposite behaviour. The certified values and their precision for certified standards are normally obtained by single element analysis and do not consider performance during time. Considering the fact that our method analyses 28 elements and that this might introduce additional variations both in trueness and precision compared to single element analysis and the fact that the results were obtained during ten month, our method is fit for our purpose to study release from materials. For legal purposes or for detailed studies on specific elements a single element analysis may be more appropriate. This is especially true for arsenic.