Liquid state of hydrogen bond network in ice
  Here we show that the Coulomb interaction between violations of the Bernal-Fowler rules leads to a temperature induced step-wise increase in their concentration by 6-7 orders of magnitude. This first-order phase transition is accompanied by commensurable decrease in the relaxation time and can be interpreted as melting of the hydrogen bond network. The new phase with the melted hydrogen lattice and survived oxygen one is unstable in the bulk of ice, and further drastic increase in the concentrations of oxygen interstitials and vacancies accomplishes the ice melting. The fraction of broken hydrogen bonds immediately after the melting is about 0.07 of their total number that implies an essential conservation of oxygen lattice in water. 
M. I. Ryzhkin, A. V. Klyuev, V. V. Sinitsyn and I. A. Ryzhkin
cond-mat.stat-mech cond-mat.other physics.chem-ph