Økologisk byfornyelse og spildevandsrensning, 48 – Brug af regnvand opsamlet fra tage og befæstede arealer

Use of Rainwater Collected from Roofs and Built-up Areas

Summary and conclusions

Identification of chemical and biological hazards as well as technical and esthetical problems are critical issues, that have to be dealt with when developing sustainable solutions for management and reuse of water, both wastewater and urban runoff. In the present study, three different possibilities for use of collected rainwater (laundry, toilet flushing and vehicle and window washing) were evaluated individually, with respect to different types of human health hazards and technical and esthetical problems.

A literature survey revealed that a total of 63 metals, 640 xenobiotic organic compounds, 33 microbiological parameters and 119 general physical and chemical parameters have either been identified or could potentially be released to the rainwater before collection. These pollutants were evaluated to determine their possible impact on health or any esthetical and technical problem during use. The hazards regarding human exposure taken into consideration were infectious diseases, cancer, allergic reactions, mutagenic changes and effects on reproduction. The technical problems considered were precipitation and corrosion, and compounds causing discoloring and odours were included due to potential esthetical problems. The evaluation showed that nine specific pathogenic microorganisms might cause infectious diseases due to use of collected rainwater. A relatively large number of metals and xenobiotic organic compounds (153) were found to be able to give allergic reactions, cancer, mutagenic changes and/or effects on reproduction. Geochemical modeling showed that there is possibility for oversaturation with a number of metal salts, which could cause both precipitation and clogging as well as discoloring of clothes.

The study showed that the approach developed during the project is promising regarding identification of hazards related to the use of collected rainwater. The method could easily be extended to include other possible uses of the water, e.g. garden irrigation or infiltration into the ground. The hazard identification should in those cases also consider environmental aspects. Introducing the probability for a hazard or a problem to occur, i.e. extending the method to include both a hazard evaluation and risk characterisation, could also extend the approach.