<p>The supply of clean and affordable water, from municipal water utilities, has continued to be irregular or unavailable in most Nigerian settlements. Also, the problem of the spatiotemporal variability of rainfall subsists. Hence, the need for alternative supplementary water sources, as well as storage. This study aims to determine the water quality of roof-harvested rainwater (RHRW) vis-à-vis the Nigerian Standard for Drinking Water Quality guideline values, to determine the relationships between the hydrochemicals in rainwater (RW) stored in plastic and steel tanks as well as to determine the effect of storage materials on the quality of RHRW. Samples of RHRW, stored in plastic and steel tanks, were collected for 75&#xa0;days at 5-day intervals. The collected data were analyzed using correlation and principal component analyses, while the water quality was assessed using the weighted arithmetic water quality index method. The results revealed that the average concentration of total iron (Fe) and lead (Pb) exceeded the NSDWQ maximum permissible limits for the water stored in the plastic and steel tanks, respectively. The average pH was acidic for all the experiments studied. The multivariate analysis yielded principal components that accounted for 99.3% and 98.3% of the variance in the RHRW quality stored in the plastic and steel tanks, respectively. Wilcoxon rank sum and Welch’s tests showed a statistically significant difference (<i>p</i> &lt; 0.05) in the harvested RW stored in both tanks for the parameters of Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl⁻, F⁻, Pb, SO₄²⁻, CO₃²⁻, HCO₃⁻, Fe, Zn, and TSS. On average, the quality of stored RW was found to range from “poor” to “unfit for drinking” The order of deterioration of water quality, based on the WQI, was as follows: steel tank stored RW (StSRW) &gt; plastic tank stored RW (PtSRW) &gt; RHRW before storage (RHRWbS). The quality of RHRW, stored in plastic and steel tanks, calls for continuous monitoring and appropriate remediation.</p>