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Many cities are facing water shortages because of climate change. Climate adaptation plans have prioritized water saving to prevent the devastating consequences of drought. To develop such adaptation plans, it is critical to understand the water-use patterns of cities. The present research determines the water consumption for irrigation of green spaces and residential gardens in metropolitan area of Santiago, Chile (MAS) and compares this consumption with the expected vegetation water requirements estimated using a hydrological model. The monthly water consumption was obtained from a database of drinking water meters provided by the private water utility serving most of the MAS, which includes 110 large parks and 1882 small parks. The MAS shows higher water consumption during the summer dry months (November to April). The water use for irrigation is higher than the modelled demand of vegetation, which entails a significant chance to save water. The irrigation rate of public spaces is lower than private spaces, and closer to the modelled demand. In all cases, the landscaping based on extensive lawn surfaces seems to be the main driver of over-irrigation. Further research is required to study the trade-offs between the urban green benefits and the costs of irrigation in semi-arid and Mediterranean cities.