ASSESSING RAINWATER QUALITY ACROSS URBAN LAND USES IN ILORIN METROPOLIS

Abstract

Rainwater can contain significant amounts of pollutants such as heavy metals, nutrients, and pathogens as a result of various anthropogenic activities resulting from land use types and population increase. This study assessed the rainwater quality of prominent urban land use types in Ilorin Metropolis, with the stated objectives: to determine the physicochemical properties of rainwater in the prominent urban land use types, to compare the physicochemical properties of rainwater in the prominent urban land use types with the World Health Organization water quality standards, to examine the variation in the physicochemical properties of rainwater in the prominent urban land use types, to identify the prominent urban land use types and to assess the urban land use changes between the year 2006 and 2020. A total of 5 rainwater samples was collected at selected locations within the prominent urban land use types and analysed for 15 major physicochemical parameters namely: colour, conductivity, pH, total dissolved solids, turbidity, aluminium (Al³⁺), copper (Cu²⁺), iron (Fe²⁺), lead (Pb²⁺), nickel (Ni), nitrate (NO₃^-), phosphorus (K⁺), sodium (Na⁺), sulphate (SO₄^2-) and zinc (Zn²⁺) using the colorimetric method, multimeter method, electrometric method, gravimetric method and atomic absorption spectroscopy. The results reveal that there is a significant relationship between the prominent urban land use types of agricultural, commercial, industrial, institutional, and residential land uses and rainwater quality in Ilorin Metropolis. Agricultural, industrial, and institutional land uses have the least significant effect on the quality of rainwater with the significant value of 0.044, 0.035, and 0.014, respectively, which is less than 0.05 degree of freedom. However, residential land use has very poor rainwater quality with a significant value of 0.724, while commercial land use has fairly good quality with 0.585, which are both above the degree of freedom of 0.05. All the physicochemical parameters tested for met the World Health Organization Water Quality Standards, with the exception of iron in the industrial and institutional land uses, which both exceeded the 3.0 mg/l value. Between the year 2006 and 2020, Ilorin’s settlement annual growth rate increased by 126%, on the other hand, the dense vegetation reduced by 41%, vegetation and farm land reduced by 68%, rock outcrop reduced by 17%, and the water body neither increased nor reduced. This study therefore recommends that rainwater should be purified appropriately before drinking, and effective, sustainable urbanization policies should be developed to prevent atmospheric pollution in Ilorin Metropolis.