Physicochemical and bacteriological characteristics of rainwater harvested from rooftops in Esan-West Local Government Area of Edo State, Nigeria

Abstract

Due to scarcity of potable water, rainwater harvesting from rooftop has been favoured as an alternative source of water supply by most rural communities in Nigeria. This study investigated the physicochemical and bacteriological characteristics of rainwater harvested from three different rooftop sheets in Esan West Local Government Area, Edo State. Parameters investigated include pH, TSS, TDS, Turbidity, Acidity, Ca²⁺, Fe, Pb, Cr, TBC, TCC and E-coli. The results showed that mean values of harvested rainwater from all sampled rooftops are acidic especially at the onset of the raining season. TSS and TDS were highest in samples collected from Asbestos rooftop, followed by Aluminum rooftop while samples from galvanized Iron had the least irrespective of the rainfall event. Rainwater samples collected at the onset of rain had higher Ca²⁺ concentration than those collected at the peak of rain for all roof type with galvanized Iron rooftop catchment recording the highest concentration. Samples collected at the onset of the rain for all roof type had Fe concentrations above the WHO limit of 0.1mg/l while those collected at the peak of rain had lesser values. Values of pb, Cr were within WHO permissible limit. Analysis of microbial parameters revealed that samples collected from all rooftop and for both seasons exceeded WHO limit of <100cfu/ml for TBC. Rainwater samples collected from corrugated Asbestos rooftop had the highest bacterial load for both onset and peak of rain, followed by samples collected from Aluminum rooftop for the onset on rain. E-coli count was highest in water sample collected from corrugated Asbestos rooftop for onset and peak of rain. The Analysis of variance (ANOVA) shows that quality of rainwater harvested from galvanized Iron, Aluminum and Asbestos rooftop catchments does not significantly differ at 0.05 statistical thresholds among rooftop catchment although samples from asbestos rooftop catchment recorded highest contamination level. In view of the physicochemical and bacteriological results, harvested rainwater can be put to all forms of domestic use except for direct ingestion unless treated.

Keyword: Rainwater harvesting, drinking-water, physicochemical, bacteriological parameters, Heavy metals, rainfall onset, rainfall peak