Chemical characteristics and microbiological loads of harvested rainwater run-off from roof tops in South Eastern Nigeria

Abstract

The study evaluated rainwater quality harvested from roof top catchments viz Asbestos, Aluminum, Corrugated and Harvey roof tops in southeastern, Nigeria. Chemical and microbiological species viz pH, Total Dissolved Solids(TDS), Electrical conductivity (EC), Nitrate(NO3−), Sulphate (SO42−), Chloride(Cl−), Total bacteria load(TBL), Total Coliform Count (TCC), Salmonella Shigella Agar (SSA), Thiocitrate Bile-salt Sucrose(TCBS), Eosin Methylene Blue (EMB) were investigated from samples of rainwater roof top run off during onset rain (April), peak rain (July) and cessation (October) rain events in 2022. Results of chemical parameters show significant variation p ≥ 0.05 among the catchments with increased mean concentration of pH(6.5), TDS(25.7 mg/l), EC(43.6μS/cm),NO3−(0.72 mg/l) SO42(4.73 mg/l), Cl(8.81) during onset rain more than the peak and cessation rain, with asbestos rainwater having the highest levels but below WHO/FMENV drinking water limit. Positive and negative correlations existed between the chemical parameters in temporal scale and originating from human activities with the temporal variability in decrease order: April ≥ October ≥ July. Microbial parameters in rainwater revealed mean TBL(6.6 × 104 cfu/ml), TCC(2.6 × 103 cfu/ml) and control (5.8 × 104 cfu/ml) with Aluminum top (8.2 × 104 cfu/ml) recording highest in onset rain more than the peak and cessation rain events. All of the microbial parameters were above the WHO standards which indicates a very high public health risk if consumed without treatment. Organisms found in rainwater from roof types are: Enterobacter sp., Staphylococcus aurous, Streptococcus sp., Bacillus Sp. and Escherichia coli. Based on the results, treatment of rainwater, operation, maintenance methods should be upheld for quality assurance of harvested rainwater.