A new photocatalytic reactor design for water treatment is presented, 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-shaped lamps coated with the catalyst showed 695% increase in efficiency of the reactor performance when compared with classical annular reactor, 260% when compared with a slurry reactor, and 60% when compared with a multiple tube reactor. The classical annular reactor and slurry reactor cannot be scaled-up for large-scale applications due to the low values of an illuminated catalyst surface area per unit volume of liquid treated inside the reactor. In the multiple tube reactor the above problem could be eliminated, but it suffers from the disadvantage that uniform light intensity cannot be achieved. Development of a reactor using the new lamps will provide all the advantages of the multiple tube reactor, plus the additional advantage that the catalyst could be activated at its highest level. The present configuration is flexible enough for large-scale applications.