Answer
Hydrogen Bonding, London Dispersion Force.
Work Step by Step
London Dispersion Forces must be overcome for water to decompose. However, the main force that must be overcome is hydrogen bonding, which results from an extremely polar bond between hydrogen and very elecronegative elements. Hydrogen bonding is the reason that water has a high boiling point compared to other molecular compounds. Note, Hydrogen bonding does not occur within molecules but between different molecules in which a Hydrogen is bonded to Nitrogen, Oxygen, or Fluorine.
