This paper presents a methodology for assessing TSS wet weather event load along with the associated uncertainties from continuous turbidity measurements. The proposed method is applied to dozens of rainfall events sampled on various urban catchments in the cities of Paris and Nantes. This method takes into account the dependency between the residual errors made by converting the turbidity values into TSS concentrations using an average TSS-turbidity relationship. Results obtained indicate that the inter-event variations of TSS-turbidity relationships induce significant systematic errors on TSS event loads which can reach ±30% of the average TSS event load.