  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.
