Knowledge about the hydrogen bond network of water is essential for understanding its anomalies as well as its special role for biochemical systems. Different types of x-ray spectroscopy allow probing of the molecular orbitals of water, revealing the electronic structure which reflects the hydrogen bond conformations. In this work a recently developed high-resolution x-ray emission spectrometer was used in combination with the microjet technique for recording spectra of liquid H 2O and D 2O and their mixtures with acetonitrile. Variation of the nuclear dynamics via isotope substitution and variation of the hydrogen bond conformation via dissolution in acetonitrile was investigated. These two effects have two clearly distinguishable spectral fingerprints.