Rainwater is increasingly being used as an alternative water source for households and industries. It can be used for a variety of purposes such as watering plants, rinsing surfaces, and, after proper treatment/disinfection, flushing toilets. Constantly decreasing freshwater resources and climate change encourage the installation of systems for collecting and using rainwater. However, it is crucial to properly select the available solutions on the market to meet consumer needs while considering maintaining the appropriate quality of collected water. This research aimed to assess the quality of rainwater collected from roof surfaces in open and closed above-ground and underground tanks. The tanks, with a capacity of 300 L, were made of polyethylene and equipped with drain valves and an opening flap. Water samples were subjected to physicochemical, chromatographic, and toxicological analyses immediately after collection and after a given period of water storage in tanks. Samples were taken every two days over four months.

It was shown that the residence time of water in retention reservoirs significantly affects the deterioration of their quality in both above-ground and underground reservoirs. It was recorded that the pH of water decreases from 7.6 to 4.3 over time. Moreover, an increase in TOC concentration was observed in both covered and open above-ground tanks. The chromatographic analysis of rainwater samples that was performed immediately after the rainfall was collected in the tanks and after a given storage period showed the presence of organic micropollutants that gradually decompose. The presence of decomposition intermediates was particularly clearly observed in outdoor tanks exposed to solar radiation. The toxicological analysis showed a change in the water from a non-toxic to a low toxic level.

Acknowledgments: This research was financed by the National Centre for Research and Development, No. LIDER13/0126/2022