Comparative assessment of the effect of storage vessels, thatched roof and industrial activity on harvested rainwater quality in south eastern, Nigeria using water quality index

Abstract

Abstract Rainwater is usually harvested through catchment systems such as roofs or directly from the sky for storage in different vessels for eventual use due to water scarcity which is as a result of increased in water demand, rapid industrialization, increasing pollution, global warming and climate change. This study was carried out to assess the effects of galvanized iron and PVC tanks, thatched roof and industrial activity on harvested rainwater quality by investigating physico-chemical properties, heavy metals, coliform level and metal composition of the storage vessels. Seven-two harvested rainwater samples were collected from four locations in the urban and rural areas of Delta and Enugu States, Nigeria between the months of April-July, 2018. Rainwater samples stored for 1 month to a year in storage vessels were considered. The results were compared with water quality standards (USEPA, WHO, NAFDAC and NSDWQ) and Water Quality Index ratings. Heavy metals (Pb, Fe, Cr, Zn and Al) were analyzed using Flame-AAS; other parameters were determined using standard methods. The WQI ratings were calculated using the weighted arithmetic method. The results were analysed using descriptive and two-way ANOVA statistical analysis. Results obtained in both areas of the States showed mean values ranging from 5.60 ± 0.28 to 7.60 ± 0.20 for pH, E.coli (0.00 ± 0.00–1.00 ± 0.00 cfu/mL), EC (7.00 ± 1.41–108.70 ± 8.62 µs/cm), colour (0.44 ± 0.01–12.86 ± 0.17 TCU) and heavy metals (mg/L) gave 0.00 ± 0.00–1.52 ± 0.13 for Fe, Pb (0.00 ± 0.00–0.29 ± 0.02), Cr (0.00 ± 0.00–0.30 ± 0.05), Zn (0.00 ± 0.00–0.05 ± 0.02) and Al (0.00 ± 0.00–4.65 ± 2.24). The results of the harvested rainwater samples analyzed showed that, the mean values of all the parameters analyzed were below and within the water quality set standard with the exception of a few in both areas in each of the States and were significantly different at (p < 0.05). The results of WQI ratings showed that, harvested rainwater qualities in both States were rated from excellent to unfit for drinking water quality. Generally, harvested rainwater stored in PVC tanks rated better than rainwater stored in galvanized iron tanks though not free of contamination. The storage duration for harvested rainwater is very important for its water quality, hence, harvested rainwater whether it is stored or not should be subjected to treatment before being use for potable usages.

Keywords

• Harvested rainwater
• Heavy metals
• Storage vessels
• Thatched roof
• Water quality index (WQI)
• Policy