Due to water scarcity, rainwater is increasingly used for both potable and non-potable purposes in Nigeria. This is due to increased urbanization, industrialization, global warming and climate change (Okudo et al., 2023) . Due to industries’ massive emissions of pollutants into the environment, urbanization and rapid industrialization have had a significant negative impact on water quality. Oil and gas industry activities and has impact negatively on water and air in Southern Nigeria. The likelihood of rainwater becoming contaminated is very high. Despite the widespread use of rainwater, especially in southern Nigeria, there is no evidence that its use is standardized for safety. Environmental pollution has affected the quality of water in general, and it also has a negative effect on the quality of rainwater. Rainwater quality is impacted by a number of factors, including animal faeces and debris on roofs, leaching roofing materials, and vehicle exhaust emissions (Zdeb et al., 2020) .

Because the place where the rain falls may have an impact on the quality of the precipitation, rainwater is not always clean and safe to drink. Emissions from houses, companies, and factories can easily dissolve in water without changing the colour or flavour and may not be physically detectable, contaminating rainwater in established communities (Khayan et al., 2019) . The community’s overall health can be impacted by the quality of the water that is available to them, and when the water is of high quality, it becomes essential for leading a productive and healthy life (Aryal et al., 2012) . Globally, Bełcik et al. (2024) reported concentrations of some heavy metals (Cu, Pb, Cr, Ni and Cu) in run-off rainwater from Białystok in Poland. Similarly, the concentrations of As, Sb, Cr, Pb, and Cd in rainwater runoff from antimony mine area in Lengshuijiang City, Hunan Province, were reported by Chen et al. (2024) . According to the authors, As and Sb pose the most serious health risks to residents in the village, with HI values of As and Sb greater than 1.

If values of the physicochemical parameters are higher than acceptable limits, humans and other living forms may be at risk for health problems (Aryal et al., 2012; Okpoebo et al., 2014) . Ebong et al. (2016) conducted research on collected rainfall from regions in the southern part of Nigeria that experience ongoing gas leaks caused by the operations of multinational oil corporations. The pH, Fe, Pb, Cd, and Ni values were above the allowable limits, and an investigation of the physicochemical characteristics and certain trace and heavy metals revealed potential health effects. According to Olowoyo’s (2011) research, the pH and total suspended solids in rainwater exceeded the World Health Organization’s recommended values. The proximity to the refinery and petrochemical company, where gases are carelessly flared into the environment, could be the cause, the authors speculated.

In their study, Imarhiagbe & Osarenotor (2020) evaluated the quality and health risk of non-roof-harvested rainwater in a southern Nigerian oil-producing community. The ranges of concentrations for iron and lead were 0.27 to 1.79 mg/l and 0.0 to 0.025 mg/l, respectively; the ranges for chromium were 0.0 to 0.028 mg/l and 0.0 to 0.021 mg/l. Fe, Pb, and Cd values are higher than the necessary tolerance level. But the health risk index is not equal to one.

The amounts of certain heavy metals found in rainwater samples, as reported by Itodo et al. (2021) . Their findings show that Pb, Fe, and Cr are present in the rainwater samples, with Pb metal being present at levels higher than the 0.3 mg/L WHO maximum allowable limit.

The quality of rainwater collected is impacted by the ongoing growth in industrial activities and population growth, both of which have a significant impact on air quality (Marlier et al., 2015) . Rainwater has the ability to dissolve different particulates and air pollutants. It is crucial to keep an eye on the quality of rainwater, particularly in industrial areas where gas flaring is a regular occurrence. The work done by Itodo et al. (2021) showed that the level of some metals is alarming. However, the health implications were not as certain. It is imperative to keep monitoring the levels of these metals and to advise relevant government bodies of the necessary actions. The goals of this investigation are:

1) To investigate the concentrations of Cr, Cd, Pb, Cu and Zn of rainwater samples collected from roof and non-roof sources.

2) Compare the physicochemical parameters of samples collected from roof and non-roof sources.

3) Estimate the health risk index (HRI).

Concentrations of Cr, Cd, Pb, Cu and Zn of rainwater samples collected from roof and non-roof sources

The results of the investigated heavy metals concentration in the harvested rainwater are presented in Figures 2-5 . Out of the four tested heavy metals, Cr, Cd, Pb, Cu and Zn were detected in all samples. The results of the current study are compared against international and local studies on the occurrence of heavy metals in harvested rainwater. In context of Jakpa, Ubeji, and Udu, the pattern in the mean concentration of Chromium (Cr), Cadmium (Cd), and Lead (Pb) were assessed based on research objective one. The results revealed that pattern and concentration of Chromium for both the non-roof and roof sources were within the World Health Organization (2004) recommended standard of 0.05 mg/L, with exception of the Jakpa which the roof source result gave 0.085 mg/L during the month of April ( Figure 2 ). The concentration of Cadmium indicated sudden increase in some localities and months well above the threshold limit of 0.03 mg/L WHO (2004) . For instance, the results from the non-roof source in Jakpa gave 0.040 mg/L for the month of August and not available for other months. However, the results from roof source gave the values of 0.035 and 0.075 mg/L for the months of April and June, which were above WHO standard. The result suggested pollution with respect to Cadmium ( Figure 3 ) especially during June ( Table 2 and Table 3 ).

The concentration of Lead as indicated in Figure 2 , Figure 3 and Figure 5 revealed that rainwater constituted serious pollution problem in Jakpa and Ubeji. The pattern of concentration in Jakpa at non-roof source (location) gave the values of 0.046 mg/L, 0.011 mg/L, and 0.081 mg/L for the months of April, August, and October 2022. The results from roof samples gave the mean concentration of 0.480 mg/L, 0.033 mg/L, 0.012 mg/L, and 0.006 mg/L for the months of April, June, August, and October which are higher than the WHO standard value of 0.01 mg/L. Thus, indicating high level of pollution. Similar perspective of Lead reflected in Ubeji roof source sample with an exception of the month of October.

The assessments of Zinc and Copper concentration in rainwater within selected locations were carried out and the results presented in Figures 2-5 . The result of Zinc concentration in rainwater at non-roof Jakpa gave the value of 0.081 mg/L ( Figure 5 ) for the month of October to a highest value of 0.567 mg/L ( Figure 4 ) for the month of August. Similar patterns reflected in roof samples with the least value of 0.152 mg/L recorded during October and the highest value of 0.610 mg/L. In Ubeji, the concentration of Zinc within the non-roof source was the lowest during the month of April with a value of 0.052 mg/L ( Figure 2 ) and the highest during the month of August with a value of 0.447 mg/L ( Figure 4 ). The results of the values from roof source ranged between 0.014 and 0.413 mg/L.

In summary, the Pb, Cr and Cd concentration in rainwater samples especially from roof top collected from Jakpa were above the threshold value reported by WHO (2004) . Other researchers such as Nicholas & Ukoha (2023) reported mean concentration of 0.07 mg/L for Pb in rainwater samples from asbestos roof. Also, Okudo et al. (2023) reported high values of 0.58 for Pb in analyzed rainwater samples from Enugu State, Nigeria. Similarly, Ayenimo et al. (2006) reported higher values of Pb from runoff water from roof which were above the set standard.

Concerning heavy metals contamination, the results of this research showed that most of the water samples analyzed were not safe. For the metals, 67%, 25% and 4% representing Pb, Cd and Cr of the samples collected for different months had values above the WHO limits. None of the samples exceeded the WHO for Zn and Cu in all months. Statistical analysis showed that there was relationship between rainwater samples from roof and non-roof top. Health risk index estimated for Cd in samples is not within safe limit. This study only presents results for heavy metals. Therefore, it is hereby recommended that other important contaminants such as PAHs, OCPs and phthalate esters should be considered for further study for drinking water safety.

All authors have read, understood, and have complied as applicable with the statement on Ethical responsibilities of Authors as found in the Instructions for Authors.

We would like to thank the Department of Environmental Management and Toxicology for their contribution in this research.

Iwekumo E. Agbozu designed the research, methodology and edited the manuscript. Tobore R. Maminor performed the experiments and collected samples, Uwem Bassey wrote the manuscript and analyzed the data.

All data generated or analyzed during this study are included in this published article.

*Values greater than WHO standards.