The first flush phenomenon can be defined as the initial period during which the concentration of pollutants was higher than those in latter stage of rain events (Gupta and Saul 1996). Researches have shown that diverting the first flush from the harvested rainwater may improve the quality of stored water. In this study, a special first flush volume harvesting system has been setup in two houses located in two different areas in the Ile de France (France) and 13 storm events during 8 months have been collected. The results show the correlation between some parameters. Amount them, TSS and turbidity show a clear decline, which have the potential to describe the first-flush effect. Otherwise, there was no evidence that can prove the existence of such first flush phenomenon in terms of the microbial indicators. The first flush effect can be also linked to the rain events factors such as rain intensity and antecedent dry time.