Tunable nanodispersions of titania as stable, cost-effective, and high-performance photocatalysts for water splitting. An important route towards making solar fuel production cost-competitive is to create photocatalysts that are stable, inexpensive, easy to synthesize, and that are active in water splitting. Here, we show that titanium (IV) chloride (TiCl4) can be used in aqueous media as a green chemical reducing agent for the synthesis of stable, easy to handle, and highly crystalline titania nanodispersions from commercial TiO2 nanoparticles. We are able to produce aqueous solutions containing stable titania nanodispersions with a broad range of sizes (40-220 nm) and narrow particle size distribution. The resulting nanodispersions are highly active for water splitting both as suspensions and under a thin film architecture. Importantly, this work shows that nanodispersions of TiO2 nanoparticles can be used as stable, easily synthesized photocatalysts for solar water splitting with efficiencies of up to 6 %, which are comparable to the efficiencies reported for bare titania nanoparticles and higher than for other carbon-based nanodispersions. Furthermore, this work highlights the great versatility of titania nanodispersions, which can be prepared in a wide range of sizes and nanodispersion stability, and as a function of particle size and surface chemistry. This work shows how using a "green chemical" approach with simple inorganic salts enables the straightforward production of high-performance photocatalysts for solar-driven water splitting. This approach could be further extended to other nanomaterials, for which a controlled synthesis could result in stable and active nanomaterials that are easy to fabricate as photovoltaics, energy storage devices, or for photocatalytic applications.