Concentrations of elements in the aquatic environment are a key parameter for various scientific fields such as biogeochemistry, biology and environmental science. Within this context, the scientific community asks for new analytical protocols to be able to quantify more and more elements of the periodic table. Therefore, the requirements for aqueous reference materials have increased drastically. Even though a wide variety of CRMs of different water matrices are available, certified values of many elements (e.g., rare earth elements (REE), technology-critical elements, such as Ga and In, and generally those elements which are not part of current monitoring regulations) do not yet exist. Therefore, the scientific community relies on published elemental concentrations of many CRMs provided by other researchers. Some elements of interest, such as the REE, are well studied and plenty of literature values exist. However, less studied elements, such as Ga and In, are rarely studied. In this study, an ‘externally’ calibrated quantification method based on an optimised online preconcentration method coupled with ICP-MS/MS was used for the quantification of thirty-four elements. The method was applied to seventeen water CRMs covering freshwater, brackish water and seawater. The measured data are combined with a comprehensive literature review on non-certified values in selected water CRMs, and new consensus values are suggested for various non-certified elements.