Bent molecular geometry of water

Could you please explain how the bent molecular geometry of water is due to hydrogen bonding? I was under the impression that it was because of the lone pairs (VSEPR Theory).




Your understanding is correct. The usual explanation given in introductory classes is [VESPR](http://en.wikipedia.org/wiki/VSEPR_theory) theory. The oxygen atom has four bond-like "things" coming out of it. Two of those are the covalent bonds with the hydrogen bonds. The other two are the two lone pairs. VESPR theory calls this a [steric number](http://en.wikipedia.org/wiki/Steric_number) of four. 


The slightly more advanced explanation comes from [molecular orbital theory](http://en.wikipedia.org/wiki/Molecular_orbital_theory). Oxygen's valence electrons are all $2\text{p}$ electrons; hydrogen's electron is $1\text{s}$. The only way to mix those orbitals to get enough bonding orbitals is by using two $\text{sp}^3$ hybrid orbitals to generate the two bonds. The $\text{sp}^3$ orbitals are arranged in a tetragonal geometry.


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