In the quest to find safe, low-cost batteries for the future, eventually we have to ask ourselves a question: Why not simply use water as an electrolyte? Water is cheap, in abundant supply, doesn’t burn and can conduct ions. But it has one major drawback: It is only chemically stable up to a voltage of 1.23 volts. In other words, a water cell provides three times less voltage than a customary lithium ion cell with 3.7 volts, which makes it poorly suited for applications in an electric car. A cost-effective, water-based battery, however, could be extremely interesting for stationary electricity storage applications.