Water’s hydrogen bond network plays a critical role in many processes, including ion dissolution, polar reagent chemistry, and protein folding. Understanding how that network fluctuates is necessary for understanding how water-influenced processes work. Previous research has shown that frozen water molecules can rearrange by rotating without breaking any hydrogen bonds or by bifurcating, in which a water molecule rotates such that a hydrogen bond to one of its hydrogens is replaced by a hydrogen bond to the other. A pair of water molecules in a cluster may also break and form two new hydrogen bonds through a tunneling mechanism in which the two molecules simultaneously rotate, according to new work by a team led by Jeremy O. Richardson of Durham University, Brooks H. Pate of the University of Virginia, and Stuart C. Althorpe and David J. Wales of the University of Cambridge (Science 2016, DOI: 10.1126/science.aae0012). The scientists studied the tunneling rearrangement in an (H2O)6 prism by using microwave spectroscopy and quantum mechanical modeling. Water in cellular or other confined environments may rearrange similarly.