Photocatalytic water splitting has been studied extensively as a promising technology for scalable and cost-efficient hydrogen production using solar energy. Although overall water splitting has been achieved under visible light irradiation, significant progress in reaction efficiencies at longer wavelengths is needed to enable practical solar energy conversion. This article reports recent advancements in kinetic investigation and numerical modeling of photocatalytic water splitting to understand problems with existing photocatalysts and develop strategies to boost the reaction efficiency. Kinetic investigation based on cocatalyst loading, light intensity, hydrogen/deuterium isotopes, and reaction temperature suggests that the majority of photoexcited carriers recombine before contributing to the water splitting reaction on the surface in most cases, and that improvement in semiconducting properties of photocatalysts by decreasing defect and donor concentrations is beneficial to boost photocatalytic performance. It is demonstrated that an appropriate material design to suppress generation of donor species actually improves photocatalytic activity. Numerical modeling of steady state carrier concentrations suggests that an asymmetric built-in potential in photocatalyst particles enhances charge separation and thus extends the lifetimes of photoexcited carriers. On the basis of the recent findings, we suggest strategies to improve the reaction efficiency of photocatalytic water splitting.