Vacuum ultraviolet photons (VUV; wavelength<200 nm) have energies greater than most chemical bond energies and thus offer a relatively simple means of degrading water contaminants via direct photolysis. Measurement of VUV intensity can be challenging, however, many available lamp sources are of unknown VUV emission efficiency. We are evaluating low pressure mercury lamps and excimer lamp systems, as well as VUV reactor configuration and process considerations, in order to improve the energy efficiency of photolytic water treatment.