In 1981 a remarkable paper by Unruh showed that a quantum emission similar to the one predicted by Hawking for black holes is expected in a seemingly completely different context, namely fluids undergoing hypersonic motion. This far reaching result opened a continuously developing field of research (the so called black hole analogue models) in condensed matter physics where, unlike gravity, the hope to perform experimental tests on these theoretical predictions does not seem so remote. In this context we have studied for the first time, using theoretical methods borrowed from quantum field theory in curved spacetimes, the backreaction this emitted radiation has on the fluid showing deep analogies with the evaporation of charged black holes.