The propagation of shock waves is an ubiquitous phenomenon in the ISM, where the sound speed is low due to the temperature and density conditions. At the younger stages of the formation of low-mass stars, observations over the past few decades have shown that the process of mass accretion is almost always associated with mass ejection in the form of collimated jets, extending from a few astronomical units up to parsecs from the exciting source. The supersonic impact between the jet and the parent cloud generates a shock front, which propagates in the collapsing interstellar gas, and also an inverse shock that propagates along the jet itself. Large cavities, called bipolar outflows, appear, that have been extensively studied through the molecular emission they generate. At the apices of these cavities, the shock wave heats, compresses and accelerates the ambient interstellar gas. As the temperature rises to a minimum of a few thousands of degrees, the energy barriers of numerous reactions involving neutral or ionized molecules can be overcome and the chemistry of certain species can be significantly altered. Similarly, processes specific to the propagation of shock waves affect the interstellar grains, leading to the injection of molecular and atomic species in the gas phase. The time-scales involved in the heating and in some of the shock chemistry processes are short (10$^2$--10$^4$ years), so the shocked region rapidly acquires a chemical composition distinct from that of the quiescent medium. As the gas radiatively cools down through mostly molecular emission, reactions with high energy barriers are no longer operative, and the chemistry is dominated again by low temperature reactions. In this talk, I will describe how the comparison between observations of this molecular emission with models can provide support to understand the physical and chemical processes at work in shock regions associated to the bipolar outflow BHR71. I will show the latest observations, describe the models that we use, and show what kind of informations their comparison infer about the shock itself, and also about the pre-shock conditions in the ambient medium. The quality of the constraints depends on the number of available observations, so I will show how SiO and H2 observations can in turn allow us to make predictions for H2O, for which Herschel observations should be available soon.