In 1995 Kevin Costner described in his film Waterworld , a world totally covered by water where people lived on floating atolls. A photograph of our future? Well, I would say not really, at least not any time soon. But it is expected that by 2050, 90% of the world's largest cities will be exposed to rising seas (UN-Habitat). The warming of the atmosphere, the melting of the ice at the poles, the erosion of the coasts, the increasingly frequent floods therefore push, in some areas of the world, to look towards these solutions.