Due to the increasingly severe restrictions in terms of CO2 emissions to be fulfilled within 2020, and the further reductions set for the following years, the Automotive field is now facing a period of intensive technological development and transformation. In the present dissertation a deep analysis of the water injection concept in SI-engines (spark ignition engines) to enhance higher efficiency, already adopted in the past mainly on aircrafts and race cars and now revisited to be applied on large-scale vehicle production, has been done. Since there is an important difference between gasoline and water properties, all the already assimilated considerations concerning both gasoline injection events and post-injection phenomena (atomization, evaporation, mixing) are no longer suitable when injecting water.