In our work, the study of detonation wave structure was performed by VISAR laser interferometer for a hydrazine nitrate/H2O (HN/water) solution and pressed HN with maximum density of 1.68 g/cm(3). The range of water concentration in which the HN/water solution detonated at a room temperature was found to be 25 - 36 wt.%. For the HN/water solution, the detonation velocity decreases linearly with increasing water concentration whereas for pressed HN, the dependence of detonation velocity on initial density is not monotonic, but has a characteristic "s"-shape. It was shown that the particle velocity profiles in pressed HN are smoother than in the HN/water solution. This means that detonation waves in the liquid HN are unstable, and the characteristic amplitude size of inhomogeneities is about 400 mu m. Optical registration of the detonation wave propagation in the HN/water solution was done by two different high speed optical recording techniques. A very poor glow of the detonation front in the visible part of the spectrum and its instability were observed. This may be due to the low temperature in the detonation waves in the water solution of HN. (C) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.