Finding a clean and renewable energy source to replace fossil fuels has attracted much attention, the past few decades, as a requirement for the sustainable development of societies. Direct hydrogen generation on TiO2 by photocatalytic dissociation of water using sunlight was already proposed more than 40 years ago. However, despite extensive work in this area, the fundamentals of the process remain ill-understood, mainly due to the lack of a proper tool to specifically explore the interface between water and TiO2. Sum frequency generation spectroscopy (SFG), is an inherently surface sensitive tool, allowing the study of the water-TiO2 interface. In a sum frequency generation process a visible and an infrared laser beam are combined at the interface and the vibrational spectrum of solely the molecules at the interface can be obtained. In this way we can specifically study the water molecules at the TiO2 surface. We present data on water in contact with TiO2 thin films at various pH values and isotopic dilution and correlate the spectral observations with surface species. Moreover, we show time-resolved SFG data after initiating the reaction with an UV pump pulse which mimics the sun light. These UV-pump SFG-probe data illustrate the first steps towards following the photo-induced dissociation of water at the TiO2 interface in real-time.