In early 2018, Cape Town, South Africa came dangerously close to being the world’s first major city to run out of water. People lined up for blocks to collect spring water. Stores sold out of receptacles like buckets and bowls. Bottled water was rationed in tourist-heavy parts of the city. April 12 was designated “Day Zero”—the day the water was expected to dry up. City officials prepared for riots, keeping army and police ready to be deployed to water collection sources. Rainfall in the region had been low for three years straight, prompting a drought. Thanks to a massive effort by city officials to enforce water conservation—including tariffs, heavy restrictions, and a new water pressure system, plus redirecting agricultural water to the city—Day Zero never came, and rainfall returned to normal shortly thereafter. The city breathed a collective sigh of relief; crisis averted. But the scare was a wake-up call, not only to Cape Town but to water-pressed cities around the world. Mexico City, Sao Paulo, Cairo, and many others are facing water shortages. As the world’s population grows and climate change pushes temperatures up, water is set to become even scarcer. If only there was a cheap, easy way to take the salt out of the billions of gallons of seawater sitting within a few hundred miles of all these cities. As it stands, desalination is expensive and energy-intensive. Getting the technology to a point where desalinated sea water is a viable option for water-starved cities is going to take years, if not decades—but teams of scientists around the world are making incremental progress, slowly moving us towards a water-abundant world.