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Although historically used in semi-arid and arid regions, rainwater harvesting (RWH) systems have increasingly been used in non-arid and humid regions of the world to conserve potable water and mitigate stormwater runoff. Rainfall characteristics and usage patterns of stored rainwater are distinctly different in (semi-)arid and humid regions, thus presenting a unique set of challenges with respect to their utilization. Coupled with infrequent use, the addition of nitrogen and organic matter via pollen during the spring season can lead to anaerobic conditions within storage tanks, which hinders nitrogen removal, gives stored water an offensive odor, and ultimately discourages use of the water. This study evaluated three measures that can be implemented for new and existing RWH systems to prevent the development of anaerobic conditions within storage tanks: first flush diversion, simulated use, and the continuous circulation of stored water. Study findings indicate that preventing anaerobic conditions via simulated use and recirculation (1) does not necessarily remedy the issue of poor aesthetics within rainwater storage tanks, and (2) can decrease the water quality benefits provided by these systems. Rather, preventing the introduction of pollen and particulate matter to the storage tank via a first flush diverter and minimizing disturbance of settled material in the tank appear to be the most effective methods of addressing the poor aesthetics and odor problems associated with anaerobic conditions.

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Highlights Rainwater harvesting systems can harbor mosquitoes and their larvae. Approximately half of sampled systems were found to contain mosquito larvae. Mosquitoes were more abundant in systems with unscreened openings and multiple inlet filters. Frequent maintenance and eliminating unscreened openings minimize mosquito presence. Abstract. Mosquitoes are associated with the spread of diseases such as the Zika and West Nile viruses. Government and health officials recommend the elimination of standing water to prevent the breeding of mosquitoes that transmit these viruses. Previous research has shown that rainwater harvesting (RWH) systems in high-rainfall regions tend to be underutilized, thereby creating a source of standing water that could potentially harbor mosquitoes and their larvae. As RWH is an important tool for conserving potable water and mitigating stormwater runoff, it is imperative to determine if these systems are contributing to the proliferation of mosquitoes and, if they are, to identify measures to prevent this. The prevalence and relative abundance of mosquitoes were investigated in 64 RWH cisterns throughout Virginia and North Carolina. Mosquito larvae captured during sampling were identified morphologically to genus and species. Of the 64 systems sampled, 47% contained mosquitoes; the predominant species found was Aedes albopictus, a potential carrier of Eastern Equine Encephalitis, LaCrosse Encephalitis, West Nile virus, and Zika virus. Systems with multiple inlet filters, unscreened storage tank openings, and/or heavy foliage in the immediate vicinity were most likely to contain mosquito larvae. Study results indicate that frequent maintenance, the elimination of unscreened tank openings, and the eradication of sources of standing water in the area surrounding a system greatly reduce the likelihood of mosquitoes proliferating in rainwater harvesting systems. Keywords: Container breeding, Mosquito, Mosquito larvae, Rainwater harvesting.