Although building materials coated with photoactive TiO₂ show remarkable self-cleaning and anti-fogging effects outdoors by absorbing UV rays from the sun, they do not function indoors. This is because the UV light intensity indoors is too weak for a simple TiO₂ coating to exhibit either photocatalysis or photo-induced hydrophilicity. In order to obtain interior photoactive building materials, herein we report three different types of materials based on TiO₂, which can function even under room light conditions. First is a TiO₂ film deposited with Cu that shows a remarkable antibacterial effect since the TiO₂ photocatalytic reaction assists the intrusion of antibacterial copper ions into cells. Thus, even very weak UV light is sufficient to lower cell activity. Second is a layered TiO₂/WO₃ heterogeneous film, which becomes highly hydrophilic even under fluorescent light since the photo-generated holes produced in WO₃ by UV light are transferred to the TiO₂ side and then used for hydrophilic conversion. Third is a nitrogen doped TiO₂ film, which can be highly hydrophilic by absorbing only visible light. In addition, we demonstrate a novel application of outdoor building materials coated with TiO₂ to environmental technology using its photo-induced high hydrophilicity. By noting that a very thin water film can form on a highly hydrophilic surface and evaporation can effectively lower the temperature by robbing the latent heat from surroundings, we proposed a novel method for cooling the surfaces of buildings and their atmospheres, i.e., a small amount of water is continuously poured onto the surface of TiO₂ coated materials. We show that this method can even reduce the temperature of a room, resulting in an energy conservation.