Mohsin Nawaz 1 Muhammad Tahir Amin 1 Mooyoung Han 2 Abdulrahman Ali Alazba 1 Umair Manzoor 1 Muhammad Nasir Amin 3 1 Alamoudi Water Chair, King Saud University, Riyadh, Saudi Arabia 2 Department of Civil and Environmental Engineering, Seoul National University, Seoul, Korea 3 Department of Civil and Environmental Engineering, College of Engineering, King Faisal University, Al-Ahsa, Saudi Arabia Research Article Variation of Pseudomonas aeruginosa in Rainwater Harvesting Systems: Effects of Seasons, Catchments and Storage Conditions The effects of different catchment types and storage conditions on Pseudomonas aeruginosa in harvested rainwater under wet and dry seasons were investigated. Both horizontal (roof intercepted to outlet point) and vertical (surface to bottom) quality variation inside storage tanks of different rainwater harvesting (RWH) systems was also monitored. The numbers of P. aeruginosa varied from 30 to 400 colony forming units (CFU)/100 mL during the dry season and 200 to 1800 CFU/100 mL during the wet season. A relatively good quality of harvested rainwater was observed in dry season. The horizontal and vertical quality variation of P. aeruginosa revealed best quality at the supply point. The number of P. aeruginosa was the highest (about 1800 and 1000 CFU/100 mL during wet and dry seasons, respectively) in rainwater harvested from mountain catchment while the lowest (about 30 and 1000 CFU/100 mL during dry and wet seasons, respectively) numbers was seen from concrete roof catchment. Dark, covered storage conditions resulting low rainwater temperatures showed better microbial quality of rainwater than uncovered and open storage conditions exposed to light. The study suggests that the improvement in the quality of harvested rainwater is possible when appropriate tank designs, maintenance of catchment surfaces, and proper storage conditions are considered in RWH systems. Keywords: Catchment type; Heterotrophic bacteria; RWH systems; Water quality; Water shortage Received: March 30, 2013; revised: May 29, 2013; accepted: July 11, 2013 DOI: 10.1002/clen.201300267 : Additional supporting information may be found in the online version of this article at the publisher’s web–site. 1 Introduction Water shortage is the major problem of this Era. Changing climate conditions and increasing demand of growing population reduced the water resources. According to the latest available information by the joint study of UNICEF and WHO, still 783 million people do not have access to safe water resources [1]. Rainwater harvesting (RWH) in this regard is reviving as a new paradigm. An efficient RWH system consists of catchment area, storage tank, supply facility, pipes and a treatment facility [2–4]. The harvested rainwater has not only been used for non-potable purposes [5, 6] but also receiving increased attention worldwide as an alternative potable water source [3, 7–10]. The poor microbial quality of harvested rainwater makes it unsafe for human use especially for potable purposes. The microbial quality of the harvested rainwater depends upon the characteristics of the harvested area, such as topography, weather conditions, and proximity to pollution sources [11, 12], the type of the catchment area [13, 14], the type of storage [13, 15], dry periods, and the handling and management of the water [11, 16]. Thus, the catchment types and storage conditions are the important factors for deciding the quality of harvested rainwater in any RWH system. The catchment surfaces can significantly deteriorate the microbial quality of rainwater especially after long dry season. Once the wet season starts, rainwater upon contact with the catchment surfaces wash many types of bacteria, algae, dust, leaves, bird droppings, and other contaminants into the water tank which in return deteriorate the microbial quality of harvested rainwater [17, 18]. This shows that along with catchment, weather conditions also affect the microbial quality of harvested rainwater. On the other hand, better storage conditions/storage tanks can be regarded as means of treatment as they offer a range of beneficial and natural treatment processes to improve the quality of harvested rainwater [19, 20]. The main focus of this study is to investigate the effects of different seasons (dry and wet), catchments (concrete roof, concrete þ green roof þ terrace and mountain), and storage conditions on Pseudomonas aeruginosa in order to lay down the proper design and maintenance guidelines for RWH systems. P. aeruginosa is an opportunistic heterotrophic bacterium which not only affects the physical characteristics such as taste, odor, and turbidity but also is Correspondence: Dr. M. Tahir Amin, Alamoudi Water Chair, King Saud University, P.O. Box 2460, Riyadh, 11451, Saudi Arabia E-mail: mtamin@ksu.edu.sa Abbreviations: CFU, colony forming unit; FF, first flush; PoS, point of supply; RWH, rainwater harvesting 1 © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.clean-journal.com Clean – Soil, Air, Water 2013, 41 (9999), 1–8