Balancing Microbial Quality and Corrosion Potential of Instantaneous, Solar, and Storage Hotwater Systems Supplied by Harveste

The acceptability of the quality of hotwater supplied by harvested rainwater in the urban environment has been the subject of much debate in many developed countries as a result of attempts to maximise usage of harvested rainwater in order to improve city water-cycle management. Debate has centred around the issues of the microbiological quality of the heated rainwater, since many tank water samples fail drinking water guidelines due to the presence of Index Organisms, and the potential acceleration of hotwater system corrosion. The problem is complicated by the availability of a number of different types of hotwater systems including instantaneous, solar-powered, and conventional storage hotwater tanks. 27 rainwater tanks and associated hotwater systems from two major Australian cities were repeatedly tested over a period of 24 months for the index and indicator bacteria E. coli, total coliform, Heterotrophic Plate Counts and Pseudomonas, along with physicochemical parameters and a variety of heavy metals. The results showed that while temperature was a significant factor for determining the microbiological quality of heated rainwater, all hotwater systems achieved large reductions of E. coli (>98%) and HPC (62-99.99%). Lead and copper were found in increased concentrations in the hotwater of the solar powered systems. However, elements thought to be possibly associated with hotwater system corrosion, such as zinc and iron, were not found to be increasing.