Situated in the alluvial plain of the Mekong river, Phnom Penh’s city has to face up every year to an increasing risk of flood. So hydraulic infrastructures have to contain the rise of the water level and to drain off wastewater and rainwater. Their absence of maintenance under regime Khmer rouge threatened the permanence of the diked city. The appeal in international expertise, reinforced from 1992, allowed the reconstruction of networks and a better valuation of vagary by the reconstitution of series of data. But the most divested populations remain the most vulnerable in inundations, always recurrent in Phnom Penh.