The current study is the most recent addition to a growing body of evidence for a new theory about the structure of liquid water. In 2004, Nilsson and colleagues sparked controversy with a paper published in Science that suggested the tetrahedral model of water was incorrect. Nilsson agrees that the debate is far from settled and that much work remains before a clear picture of liquid water emerges.

"Over the last decade or so we have discovered that materials once considered homogeneous exhibit complex nanoscale order," said Stanford Synchrotron Radiation Laboratory director Jo Stöhr. "In my view, the work on water is yet another example of the actual complexity of matter, this time within a simple liquid. Modern X-ray work appears to be triggering a new understanding of liquids and we may have only seen the beginning of a paradigm shift in our understanding."