Providing the sustainable development goals (SDGs) water, food and energy security to cities relies strongly on resource use outside city borders. Many modern cities have recently invested in a sustainable urban water system, and score high in international city rankings regarding water management and direct urban water use. However, these rankings generally neglect external resource use for cities. Here we quantify the water resources related to food consumption in thirteen cities located in Mediterranean countries, by means of the water footprint (WF) concept. These WFs amount from 3277 l per capita per day (l/cap/d) to 5789 l/cap/d. These amounts are about thirty times higher than their direct urban water use. We additionally analyse the WF of three diet scenarios, based upon a Mediterranean dietary pattern. Many authors identify the Mediterranean diet as cultural heritage, being beneficial for human health and a model for a sustainable food system. The first diet scenario, a healthy Mediterranean diet including meat, leads to WF reductions of − 19% to − 43%. The second diet scenario (pesco-vegetarian), leads to WF reductions of − 28% to − 52%. The third diet scenario (vegetarian), leads to WF reductions of − 30% to − 53%. In other words, if urban citizens want to save water, they need to look at their diets.

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