The paper presents simulation and experimental results of the effects of intake water injection on the main combustion parameters of a turbo-charged, direct injection spark ignition engine. Water injection is more and more considered as a viable technology to further increase specific output power of modern spark ignition engines, enabling extreme downsizing concepts and the associated efficiency increase benefits. The paper initially presents the main results of a one-dimensional simulation analysis carried out to highlight the key parameters (injection position and phasing, water-to-fuel ratio, water temperature and pressure) and their effects on combustion (in-cylinder and exhaust temperature reduction, knock tendency suppression, …). The main results of such study have then been used to design and conduct preliminary experimental tests on a prototype direct-injection, turbo-charged spark ignition engine, modified to incorporate a new multi-point water injection system in the intake runners. The experiments allowed to validate the model results, demonstrating the effectiveness of the proposed technology, and to further investigate on the mechanisms that allow controlling efficiency, thermal load and knocking tendency by varying the water-to-fuel ratio.