The hybridization of oxygen is $sp^3$ and the three dimensional structure is shown in the picture.
Work Step by Step
The hybridization is $sp^3$ because there are four domains around the Oxygen: two lone pairs and two bonds. The three dimensional structure is shown in the picture. There are 4 domains around Oxygen so its electronic geometry is tetrahedral. As it is tetrahedral the bond angles should be 109.5 but the bond angle for water is 104.5. This is because the lone pairs on the top of oxygen push the hydrogens down and this reduces the angle to 104.5.