Today, rising sea levels place coastal cities under constant threat. An estimated 250 million people currently live on land below projected annual flood levels, often in coastal cities such as London, Lagos, Mumbai or Shanghai; and this number may rise to 630 million by the end of the century. An additional 318 million people have been displaced since 2018, due to climate disasters. Could it be that, instead of humankind fleeing from water, building on it could serve as a better long-term solution? What would the creation of entire water cities entail for societies, economies and the environment? What if populations could live on water instead of facing displacement and migration? The combined effects of climate change, land subsidence and accelerated urbanisation could force us to rethink the use of water surfaces on Earth as potential settlement areas, as an alternative to an Earth surface made uninhabitable by over-population and climate catastrophes.