Quality of rainwater and reclaimed water used in buildings and selection of appropriate indicators.

Objectives: The use of alternative water sources such as rainwater or greywater (i.e., wastewater excluding water from toilets) for non-potable purposes may save water but, on the other hand, can also pose health risks to users. The main health risks come from microorganisms (such as bacteria, viruses, fungi, and protozoa). This work aims to analyse especially microbiological quality of rainwater and greywater used inside buildings in detail and to expand the existing knowledge about the potential health risks associated with these alternative water sources. It also considers methodological problems during E. coli and coliform bacteria detection. The final objective is to discuss requirements and appropriate indicators for monitoring recycled water quality.

Methods: We examined 30 buildings with non-potable water systems in the Czech Republic and analysed a total of 137 samples of rainwater and 120 samples of greywater. From these 30 buildings, eleven, 5 of which used rainwater and 6 of which used greywater, were sampled regularly for 1-2 years for basic chemical parameters, various faecal indicators, C. perfringens, Legionella spp. and P. aeruginosa. Occasionally, samples were analysed also for the presence of environmental mycobacteria, amoebas, viruses, and selected pathogens.

Results: Nearly three quarters of rainwater samples contained the faecal indicators E. coli or enterococci, or both, and in samples from several buildings also Clostridium perfringens was repeatedly detected. Untreated and treated rainwater were in respect to microbiological quality similar, suggesting that treatment processes were not very efficient. In greywater samples, beside faecal indicators, also P. aeruginosa and thermotolerant amoebas were repeatedly detected. Treatment technologies used for greywater were more efficient than those for rainwater systems.

Conclusion: Based on the results we evaluated appropriate indicators for monitoring recycled water quality and drafted the first Czech regulation for non-potable water.