  Interpretation of the X-ray spectra of water as evidence for its asymmetric
structure has challenged the conventional symmetric nearly-tetrahedral model
and initiated an intense debate about the order and symmetry of the hydrogen
bond network in water. Here, we present new insights into the nature of local
interactions in water obtained using a novel energy decomposition method. Our
simulations reveal that while a water molecule forms, on average, two strong
donor and two strong acceptor bonds, there is a significant asymmetry in the
energy of these contacts. We demonstrate that this asymmetry is a result of
small instantaneous distortions of hydrogen bonds, which appear as fluctuations
on a timescale of hundreds of femtoseconds around the average symmetric
structure. Furthermore, we show that the distinct features of the X-ray
absorption spectra originate from molecules with high instantaneous asymmetry.
Our findings have important implications as they help reconcile the symmetric
and asymmetric views on the structure of water.
