Increasing water demand and water scarcity around the world requires the development of robust and efficient methods for water purification in the coming decades. Here, we report a photocatalytic water purification method using visible light (532 nm) utilizing 5 nm gold nanoparticles and their enhancement when attached on the surface of silica nanospheres as an inactive support to prevent nanoparticle coalescence or sintering. This is a non-toxic, low-cost, and easy photocatalytic process which provides high decomposition rates. Decomposition of the methyl orange dye is tested as a reaction model and trichloroethylene is selected as an example of a real water pollutant. When irradiated at their plasmon resonant frequency, the gold nanoparticles generate hydroxyl radicals that degradate organic pollutants into non-toxic molecules representing a basic mechanism of photocatalytic water purification.