The present application relates to a steam iron (1) for treating garments, comprising a heel (2) to rest the steam iron (1) on a supporting surface (S) when the steam iron (1) is not treating garments, a pressurization unit (3) having a chamber (4) comprising a water inlet (5) for receiving water and a water outlet (6). The pressurization unit (3) is adapted so that, in a rest position (PI) where the heel (2) is placed on the supporting surface (S), it generates an air vacuum in the chamber (4) to draw water into the chamber (4) via the water inlet (5) and, in a lifted position (P2) where the heel (2) is not placed on the supporting surface (S), pressurizes the water drawn in the chamber (4). The steam iron also comprises a steam engine (7) for generating steam from water towards the garments and a water output channel (8) for carrying water under pressure from the water outlet (6) to the steam engine (7). This invention allows easily pressurizing the water in the chamber for in turn increasing the steam generation.