A review on physicochemical and microbiological contamination of roof-harvested rainwater in urban areas

This work proposes to consider the quality of roof-collected rainwater as the sum of three main stages. In the first one, rainfall washes out the urban atmosphere and scavenges contaminants from aerosols, gases and thin volatile particles. The second stage refers to the catchment, in which occurs contamination due to the wash-off of particles settled on the roof’s surface as well as the scavenging of roofing materials. The third stage refers to the first-flush, storage and plumbing system. In each stage, different processes take place and add specific contaminants to the initial precipitation. Only in the third stage, after the discard of the high-polluted initial rainwater, some physical processes (sedimentation and pH increase) can also improve the quality of the rainwater harvest. With this approach, it is offered a clear view of the overall contamination processes that take place in a rainwater harvesting system.The most common microbiological and physicochemical contaminants that can be found in rainwater harvesting system were regarded, together with the eventual presence of waterborne pathogens and emerging chemical contaminants, according to an extensive review of 172 previous scientific and technical works.