Evaluation of the effect of different conventional roof types and industrial activity on harvested rainwater in Southern Nigeria

Abstract

Harvested rainwater is still the only source of acceptable drinking water for rural communities in Nigeria and in some countries, where there are no water networks and it is the rooftop rainwater harvesting that is being exercised for the potable and non-potable usages. This study was aimed at evaluating the effect of roof types and industrial activity on rainwater quality by analysing the physico-chemical/bacteriological characteristics, heavy metals and investigating the metal composition of the roof types. Rainwater was harvested from long-span aluminium, asbestos, corrugated iron, Cameroon zinc, stone-coated tiles roof run-offs and directly from the sky in the urban and rural areas of Imo State between the months of April-July, 2017. The results were compared with water quality standards (NAFDAC, USEPA, WHO and NSDWQ) for drinking water and Water Quality Index (WQI) ratings since there is no standard for rainwater quality. Roofs ages from < 5, 5–10, 15–20, and > 25 years in use were considered. Heavy metals were analysed using Flame-AAS; other parameters were analysed using standard methods. The WQI ratings were calculated using the weighted arithmetic method. Results show mean values ranging from 5.70 to 6.60 for pH, E.coli (not detected) and heavy metals (mg/L) burden of 0.00–0.09 for Pb, Cr (0.00–0.79), Zn (0.00–0.06), Fe (0.00–0.50) and Al (0.00–0.63). The WQI ratings gave excellent water to unfit for drinking water quality in both urban and rural areas. Since the harvested rainwater was not free of contamination, a few helpful recommendations were suggested for positive impacts in Nigeria as a whole.