The oceans store plenty of water, we will just have to extract the salt. Ya, and build more reservoirs, poorer countries are going to get hit really hard.
Sun automatically extracts salt-free water via evaporation, then the vapor is conveniently carried by winds all over the world and literally rains from the sky.
But without vastly overengineered projects, how would we find out about the massive geniuses like Elon Musk among us? /s
You don’t even need that. Just look at Tokyo’s sewer system with huge cavernous water storage to avoid flooding.
But can we build enough reservoirs to store evaporated water? It seems like desalinization will still be important.