Rooftop-harvested rainwater for household use need not be as pure as one likes to believe.

The water may contain multi drug-resistant bacteria and animal faecal materials in them, a group of researchers has recently found out.

A scientific analysis on harvested rainwater by A. A. Muhammad Hatha, K.M. Mujeeb Rahman and Lal Deepu of the School of Marine Sciences of Cochin University of Science and Technology and Y. Jesmi and S. Jyothi of the School of Environmental Sciences of Mahatma Gandhi University, Kottayam, found that that the rooftop-harvested rainwater stored in tanks does not often meet the bacteriological quality standards prescribed for drinking water.

Bacteriological and chemical parameters of 25 samples of rooftop-harvested rainwater stored in Ferro cement tanks were analysed for the study.

Researchers have found that 50 per cent of samples of harvested rainwater for rural and urban community use and 20 per cent samples for individual household use showed the presence of E. coli, indicating faecal contamination. Faecal coliform/feacal streptococci ratios revealed non-human animal sources of faecal pollution, they said.

While E.coli was isolated from two of the nine rooftop harvested rainwater samples for household use, water from half of the storage tanks for community use in rural and urban areas showed the presence of the microorganism. The harvested rainwater for urban community use had more diverse bacterial flora when compared to that of rural areas, the paper said.

The findings of the analysis would be presented at the international symposium on health-related water microbiology that began at Brazil, Dr. Hatha said.

The study was also published in the Journal of Environment Health brought out by the National Environmental Health Association, Denver.

Rainwater harvested and collected in Ferro cement tanks was taken for analysis from rural and urban areas of Kottayam, Alappuzha and Ernakulam. Nine tanks for individual household use and eight for rural and urban community use were selected at random for the study.

The analysis was carried out to determine the “bacteriological and nutrient quality of rooftop harvested and stored rainwater for individual household use as well as for community use in rural and urban settings”.

Researchers have found that all physicochemical parameters except the pH and lower Dissolved Oxygen levels were found within the limits prescribed by the World Health Organisation. General bacterial flora of rooftop-collected water was characterised and the risk assessment of these strains was carried out by drug resistance analysis.

The outcome of the analysis attains significance in the wake of efforts of the State government to promote rainwater harvesting in the State. The rainwater harvesting system has also been made mandatory for big residential flats and commercial structures.

The paper said that “risk assessment of bacterial isolates from the harvested rainwater showed high resistance to ampicillin, erythromycin, penicillin, and vancomycin. Multiple Antibiotic Resistance indexing of the isolates and elucidation of the resistance patterns revealed that 73% of the isolates exhibited MAR.”

Overall antibiotic resistance was higher among isolates from urban samples. Resistance to antibiotics such as ampicillin, erythromycin, penicillin and vancomycin was frequent among the bacterial isolates from harvested rainwater.

Researchers suggested disinfection measures before using the rain-harvested water for drinking. For preventing coliform contamination in rainwater harvesting system, the catchment areas need to be kept clean, they said.

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