The UVA-irradiance in Fig. 3, Fig. 4, Fig. 5 and Fig. 6 showed similar variations over the experimental time. The experiments started with low morning irradiance and reached maximum irradiance (between and) at solar noon between 13:00 and 14:00 o' clock, local time. After the maximum the irradiance got continuously smaller to values similar to the beginning of the experiment. It can be observed that the inactivation kinetics does not follow the irradiance intensity, as the fastest inactivation does not coincide with the highest solar irradiance. Former works have studied the dependence of solar irradiance (intensity) and disinfection yields for solar and solar photocatalytic disinfection with the semiconductor catalyst TiO2 (Sichel et al., 2007b and Sichel et al., 2007c). Following the findings of these former works we expect also this process to start after having received a certain minimum UVA dose for inactivation. Before this dose is received the disinfection does not start, and after it continues almost independently from the incoming solar irradiance. This also explains the inactivation kinetics in Fig. 3 and Fig. 5 which show a shoulder or lag phase before the inactivation starts and then a steep slope of the curve until the detection limit is reached. This shoulder can so be attributed to the resistance of the fungus spores to oxidative stress. The higher the initial H2O2 concentration, the faster fungal resistance was overcome and the decrease in viable CFU started earlier