The photochemistry of a supramolecular system consisting of a (truncated) chlorophyll, benzoquinone and water has been explored with ab initio computational methods. It is shown that this photosynthetic model system can split a water molecule upon the absorption of a visible photon via an electron-driven proton-transfer process. It is suggested that the coupled transfer of an electron and a proton in hydrogen-bonded systems is mechanistically superior to electronic charge separation in covalently bonded donor-bridge-acceptor systems.