During the last decades a big gap has opened between onomastics on the one side and Indo-European linguistics on the other, because the progresses made in Indo-European linguistics have not been integrated into the study of onomastics any longer in a sufficient way. The article tries to close this gap by giving an outline of some of the main features of modern Indo-European linguistics. Those features are then used to reexamine the etymologies of several presumably rather old river-names and of one of the Indo-European words for "water". This sometimes leads to a reevaluation of existing etymologies. The author hopes that this article might be seen as an incentive for researchers in onomastics to care more about the findings of Indo-European linguistics again.