In general it can be observed that the inactivation curves found for well water are similar to distilled water, but require higher H2O2 concentrations to reach similar disinfection yields than in the distilled water experiments. Competitive oxidation reactions in the well water matrix cannot be excluded but dark consumption of H2O2 was higher in distilled water with 2.3 mg/L than for well water with 1.3 mg/L. This excludes an important contribution of side reactions to the H2O2 consume. The lower H2O2 concentrations in distilled water could also indicate that a certain osmotic stress exists on microorganisms. In the case of F. solani, permeability of the fungal spore cell wall could increase in distilled water, leading to faster influx of H2O2 into the cells. Especially in CPC experiments the viability of microorganisms has been notably decreased probably due to damage to the cell wall osmo-regulative system ( Sichel et al., 2007c).