This answer is not correct. Pairs of electrons occupy a reasonable amount of space and repel each other as well as attached atoms. You must have a hybrid orbital for each atom and for each pair of electrons so that the geometry of the orbitals matches as close as possible the geometry of the attached atoms and electron pairs. These atoms and pairs of electrons push each other as far apart as possible...in this case, the geometry is tetrahedral. The bond angle for the atoms in water is 105 degrees because the non-bonded electron pairs are held a bit closer to the oxygen nucleus than the hydrogen atoms and force the hydrogen atoms a little closer together than the expected 107.5 degree bond angle.