A novel photocatalytic reactor design for water treatment is characterized by the use of new extremely narrow diameter lamps, thus allowing for much higher surface area for catalyst coating per unit reactor volume and consequently for much higher specific reactor capacity. Experiments in a reactor containing 21 novel U-shapen lamps coated with catalyst showed a 695% increase in efficiency of the reactor performance in comparison with a classical annular reactor and 259% in comparison with a slurry reactor. Both a classical annular reactor and a slurry reactor cannot be scaled up for large-scale applications due to the low values of illuminated catalyst surface area per unit volume of liquid treated inside the reactor while this configuration is flexible enough for large-scale applications.