The Lake Neusiedl is a sodic lake having great sensibility to actual hydro-meteorological conditions. The water level and salt content of the water depend on the characteristic weather conditions. The Austrian part of the lake has large open water area while the Hungarian part of it has a mosaic-like structure mostly covered by reed stands. During the first years of the 21st century due to a dry period the water level of Lake Neusiedl dropped considerably. During this time considerations on possibilities on the use of external water sources for artificial endowment of Lake Neusiedl were intensified. Several studies related to this subject were performed (Donabaum & Wolfram, 2004; Kromp-Kolb et al., 2005; Verbundplan, 2005; Kubu, 2006). In the last years due to increasing precipitation the water level of Lake Neusiedl is rising again and it is rather clear that at the moment no endowment is needed. Nevertheless, possible impacts of climate change might lead to an increasing probability of dry periods lasting some years and thus might increase the probability of very low water levels on the lake or might even lead to falling dry of the lake. As sources for artificial endowment bank filtered water from river Danube or water from river Raba are considered. In this project the question how endowment with water from river Raba would influence on the water quality of Lake Neusiedl should be answered, which is a further step in the process of evaluation of the possibilities of artificial endowment of the lake.