This study investigated the efficacy of low-pressure ultraviolet (UV) irradiation and the synergistic effect of UV/titanium dioxide (TiO(2)) photocatalysis on Cryptosporidium parvum oocyst inactivation. At UV doses of 2.7, 8.0, and 40mJ/cm(2), oocyst inactivation was 1.3, 2.6, and 3.3log(10), respectively. Reactive oxygen species (ROS) generated by longwave UV radiation (>315nm) and TiO(2) achieved less than 0.28-log inactivation. However, the synergistic effect of germicidal (254nm) UV and TiO(2) resulted in 2-log and 3-log oocyst inactivation with 4.0 and 11.0mJ/cm(2), respectively. Therefore, using TiO(2) in combination with UV reduced the dose requirement for 3-log inactivation by 56%. An approximate 1-log decrease in inactivation of oocysts was observed with nanopure water in comparison to buffered water, whereas changes in pH from 6 to 8 had little effect on the photocatalytic inactivation of oocysts in either matrix (P>0.1).