To search the water model parameter space for a better water model using the MADS algorithm, we must initially set parameter bounds. Proper bounds are set so that the probability of finding a water model outside the space set by these bounds is negligible. We propose that the liquid phase geometry should not be very different from the gas phase. Therefore, we start by defining the parameter search space for molecular geometry by estimating geometry of water molecule in the vapor phase using quantum mechanics. ab initio quantum mechanical (QM) methods can give the geometry and charges which minimize the potential energy for a water molecule in gas phase 2.