Impact des pratiques d'entretien des toitures sur la qualité des eaux de ruissellement

Roof runoff harvesting and reuse have enjoyed a widespread success among private individuals in the last few years in France. This development, however, has not been brought about after much discussion on the quality of the collected water. Yet, roof maintenance requires biocides to fight against surface vegetal growth and the main component of these products is benzalkonium chloride. This paper shows that the first rain after roof treatment is extremely contaminated by benzalkonium with a concentration between 3 to 30 mg/L, depending on the roof material. These concentrations remain high even after more than 50 mm of cumulated rain. Consequently roof treatment is posing a risk for roof runoff reuse.