Standard chemistry teaches that the water molecule (H2O) is bent to 104.45 degrees due to "Lone Pair Repulsion" acting on the ideal tetrahedral angle (109.47 degrees). However, this repulsive force is currently treated as an arbitrary variable. This paper serves as Flagship Paper #4 of the 16Pi Initiative. We demonstrate that this deviation is not random, but is the result of a specific compressive force exerted by the Vacuum Modulus (16/pi). By defining the vacuum as a pressurized lattice with a geometric stiffness of 16/pi (approx 5.09 degrees of arc), we accurately predict the bond angle of water by simply subtracting one unit of pressure from the ideal tetrahedral slot. Key Findings: The "Lone Pair" is identified as an Empty Facet vulnerable to vacuum pressure. Calculation of the "Lattice Crush" force: 109.47 - (16/pi) = 104.38 degrees. Accuracy: The predicted value matches the experimental bond angle of water (104.45) with 99.93% accuracy. Appendix: Includes the Python verification script (lattice_bond_geometry.py) visualizing the geometric subtraction.