To achieve the goal of climate neutrality in aluminum casthouses, all furnaces currently heated with fossil fuels should be able to be switched to hydrogen burner technologies in the future. This primarily entails a change in the furnace atmosphere. In addition to the elimination of CO2 emissions, increased water vapor contents must inevitably be expected when combusting H2. While the oxidation-inhibiting effect of carbon dioxide on aluminum-magnesium melts is well known and extensively studied, the effects of water vapor on oxidation behavior are still largely unexplored. Depending on the burner setup, H2O contents can range from 17 vol.% (CH4 + Air) to theoretically over 95 vol.% (H2 + O2). In this work, an isolated examination of the influence of H2O on the oxidation behavior of molten AlMg alloys takes place. In addition to gravimetric analyses, an optical investigation of the resulting oxide layers is also carried out. It can be shown that high H2O contents in the furnace atmosphere have a similar oxidation-inhibiting effect compared to CO2.