Aggregation affects the stability of the nanoparticles in fluids. For hydrophilic particles in aqueous suspensions, zeta potential becomes a common measure to control the stability of the particles. However, it is not clear how zeta potential impacts on the interaction of the particles during their close range contact when the hydration repulsion arises strongly. This article demonstrates a method that uses the kinetic theory of aggregation for an aggregation system of changing zeta potential to determine the hydration repulsion and the aggregation efficiency. It was found that the hydration repulsion has an equivalent electrical potential of 30 mV on the stem surface of the particles and an exponential decay length of 2.77 Å. This hydration potential is equivalent to 12 mV zeta potential and contributes 29% to the aggregation coefficient that is 5.5 × 10-6 for a 30 mV zeta potential stabilized silica particle suspension.