Water recycling using permeable paving as the source: biological water safety and the fate of introduced microbial contaminants

Ernest Nnadi, Dr Stephen J Coupe, Oyekemi Oyelola

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review


The recycling and reuse of rainwater, using permeable paving as the reservoir for storage, shows great potential in the reduction of mains water use for low grade uses. Water for toilet flushing, landscaping and car washing can be stored in the pavement structure and pumped out for reuse. However, very little data has been made available on the potential risks to humans from the microbiological contamination of this water. This paper reports on the response of Aquaflow permeable paving to simulated contamination episodes by bacterial pathogens and facultative protist parasites, both of which could plausibly be found in permeable paving under ‘normal’ conditions, or when occasional faecal contamination occurs from animal wastes. Escherichia coli 418 was added at a density of 2.0x109 to permeable pavement models and washed through with a high intensity rainfall. Removal efficiency of the bacterium after contact with the pavement materials was around 80% following the initial rainfall event and the cell density of E. coli in pavement effluent declined rapidly in the first 3 weeks. A simultaneous increase in the number of naturally occurring protist predator organisms was thought to be partially responsible for this reduction. Culturing of effluent on a medium that was selective for coliform bacteria (Eosin Methylene Blue Agar, EMBA) showed almost complete removal of E. coli by week 9 of the experiment, with concentrations below background levels. In a separate experiment, the protist Acanthamoeba polyphaga, known to be implicated in opportunistic ocular infections, was added to pavement models in bulk and its survival analysed. Despite the supposed suitability of this organism to the permeable paving habitat, a rapid decrease in the density of A. polyphaga was observed in culture and in the rig materials that composed the pavements. These results indicate that the Aquaflow system is not necessarily a favourable reservoir for such potential disease causing agents and that such organisms, even if adapted to the pavement habitat may be removed by the ‘normal’ processes of feeding, competition and decomposition going on in the pavement. Further research and communication, with the authorities responsible for the provision of guidance on such public health matters, will assist in determining the levels of risk to humans associated with the reuse of rainwater from such storage areas and any necessary mitigation of these risks.
Original languageEnglish
Title of host publication11th International Conference on Urban Drainage, Edinburgh, United Kingdom, 31/08/08
Publication statusPublished - 5 Sept 2009
Event11th International Conference on Urban Drainage (ICUD) - Edinburgh, United Kingdom
Duration: 31 Aug 20085 Sept 2008


Conference11th International Conference on Urban Drainage (ICUD)
Country/TerritoryUnited Kingdom


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