Despite the ubiquity of electronic information, the use of printed paper continues to present a major environmental problem. Now, Minjie Li and Sean Xao-An Zhang of Jilin University in China and colleagues report the development of a new rewritable paper that contains hydrochromic molecules—dyes that turn colors when exposed to water. Pages impregnated with the dyes can be printed using ordinary ink-jet printer technology by replacing the ink in cartridges with water. The dyes can be “erased” with mild heat, and the paper can be reused dozens of times (Nat. Commun. 2014, DOI: 10.1038/ncomms4044). Yadong Yin, a nanomaterials expert at the University of California, Riverside, who was not involved in the research, says the technology is important not only to research on chromic materials but “also to the modern society, as it may help better preserve natural resources and at the same time significantly reduce the negative impacts of conventional printing technologies on the environment.” The authors culled dye candidates from several classes of compounds—oxazolidines, oxazines, and spiropyrans—that need only water to switch from closed-ring forms to open-ring, colorful isomers.