Micropollution of rainwater collected from roof surfaces in the context of sustainable water management

Rapid and often uncontrolled urbanisation, population growth and concentration in urban zones, inadequately sized water infrastructure, increasingly frequent violent weather events, atmospheric pollution, irrational fertiliser management and eutrophication are causing a number of problems including shortages of clean water and water resources and deteriorating water quality. Therefore, one of the primary objectives of sustainable development is to ensure access to water and sanitation for all through sustainable water resource management. The rainwater harvesting system is seen as an alternative source based on green technology, a closed loop economy, environmentally friendly and sustainable. The safe use of stored rainwater, regardless of technical or environmental conditions, is only possible after treatment. It is therefore important to fully understand the nature of the pollutants or the physical properties of rainwater, as this knowledge is the basis for determining the possibility of use or the appropriate treatment technology. The aim of the study was to determine the quality of rainwater collected from roof surfaces and the possibility of using them for various purposes in the broadly understood economy. The study also identified possible measures to treat rainwater for the indicated purposes. The study was carried out between 2023 and 2024. Samples of rainwater runoff from concrete tiled roofs were examined for physical properties and the presence of chemical and microbiological contaminants and microplastic particle content. Physical and chemical determinations included: turbidity; pH; conductivity; concentrations of ammonium ions, nitrate, nitrite, manganese, iron and chloride; and total hardness and alkalinity. In addition, the content of selected heavy metal ions was determined by X-ray spectrometry and the content of microplastic particles using a Laser Direct Infrared (LDIR) chemical imaging system. Studies of biological micropollutants were carried out using culture methods and included the determination of total bacterial counts at 36°C and 22°C, coliforms, Escherichia coli, enterococci, Pseudomonas aeruginosa and Clostridium perfringens. In addition, the potential cell count of living microorganisms was determined by flow cytometry. The results of rainwater quality were compared with Polish and European standards for drinking and special purpose water. The study shows that collected rainwater is characterised by good organoleptic, physicochemical and microbiological properties, and in some cases meeting drinking water standards. However, exceedances of the permissible values, mainly of ammonium ions and of the indicator bacteria and total bacteria count, were usually observed. This does not, however, rule out the use of rainwater for economic purposes, but only indicates the direction of action with regard to its treatment or disinfection.