1 Introduction

Short water supply for residential and other applications in rural and urban areas remains a major challenge facing the world today especially in developing countries like In Sub-Saharan Africa, Nigeria [1, 2]. At least 4 billion humans worldwide are unable to obtain clean drinking water, or water that is deemed hazardous to consume in the absence of point-of-use treatment facilities [2, 3]. By 2050, approximately 57% of global population would reside in areas with limited water resources [4] Only 20% of rural people and 70% of urban people worldwide have access to clean drinking water [5]. In Africa, it is estimated that 52 percent of Sub-Saharan Africans especially Nigerians lack access to portable drinking water supplies [6] and about 73% of them lack proper sanitation as wastes around their surroundings end up polluting the available water thereby leading to water poverty [7, 8]. This is because majority of Sub-Saharan African countries are located in river basins with limited water resources, while poor potable water distribution has resulted in water shortages in regions where fresh water supplies are abundant [9]. The increasing population and industrialization, in close couple with decreasing and very unpredictable precipitation pattern caused by changing climate is responsible for the strain on water consumption for household, agricultural, and industrial uses, particularly in West Africa [10] As a result of scarce water supply needed for multifarious use at the urban and rural regions of Africa, many women, young people and children in their productive age, resort to different water sources like from Harvested rainwater/Rainwater harvesting (HRW/RWH), sources etc. without any attention to public health risk that may be associated with using such water sources.

Rainwater harvesting (RWH) or Harvested rainwater (HRW) as interchangeably used in this text refers to the collection, storage, and utilization of rainwater for home, industrial, and livelihood purposes wherever and whenever it falls [6, 9, 11]. It is the collection of rainwater from catchment surfaces including roof tops and ground surface and its storage inside reservoir tanks (whether on ground surface or subsurface) before it goes into run off. Concrete, galvanized, corrugated iron sheets, thatch, tile, corrugated plastic, asbestos cement sheets, or clay are examples of roofing materials or roof tops where rain can be harvested [12].

Harvested Rainwater (HRW) from roof run off may contain certain chemical and microbiological contaminants that renders it unfit and unportable thereby posing potential public health risks to users [13,14,15,16,17,18]. Nutrients, heavy metals, and organic substances such as hydro carbonic petrol are examples of the conventional chemical contaminants, whereas pathogens and disease vectors are examples of microbial contaminants [9, 19,20,21]. In addition to traditional pollutants, developing pollutants such as pharmaceuticals and hormonal or endocrine-chemicals that can cause disruption [19, 20] and nanoparticles [22] were initially suspected to be present in rainwater runoff, however, there is insufficient data on that aspect and so needs a bridge and or research attention. There is need to mention that the source, nearby human activity, flow routes, and environmental interactions will all have a significant impact and or determine the pollutants and pollutant levels in roof water [23]. Additionally, the quality of rainwater collected from urban rooftops is impacted by roof types, age, atmospheric deposition, and weather patterns [24].

Consumption of untreated (HRW) has been noted to pose danger to public health all over the world. According to several studies, HRW may be rendered unfit for consumption by bacteria thereby posing a risk to the public’s health if consumed without being treated [25,26,27,28,29,30,31,32,33,34,35,36,37,38]. Some of the bacteria linked include Campylobacter and Salmonella, Legionella-caused bacterial pneumonia, Clostridium-caused botulism, tissue helminths, and protozoal diarrheas caused by Giardia and Cryptosporidium [37] According to World Health Organization (WHO), HRW may contain E.coli, salmonella and other diarrhea causing bacteria [39].

Water-borne bacteria, viruses, and protozoa have caused numerous outbreaks [40]. In emerging nations like Africa, millions of people suffer from water-borne infections [41]. The World Health Organization (WHO) posits that 1 of every 5 infant deaths especially between age bracket 1 to 5 in sub-Saharan Africa is associated with inadequate wash [39]. According to United Nations Children's Emergency Fund, about 4000 children pass away per day globally due to preventable contaminated water causes [42].

In order to meet the Millennium Development Goal no 6 of access to safe drinking water, HRW becomes one of the alternatives to explore in actualizing this goal. However, quality improvement must be of utmost focus while exploring this water source. This is because water quality improvement can cut the world illness burden by around 4%. [43]. As a result, adequate inquiry is required on the quality of HRW water consumed by communities in Sub-Saharan Africa like Nigeria. Presently in Nigeria, government provision of pipe borne water is yet to be accomplished and or reactivated in many states of the federation. In Umuahia located In South eastern region of Nigeria, there is none existing government provided pipe borne water except borehole source in few communities. Source of water in this region is mainly from rivers, HRW, streams and borehole water sources. The rural and urban communities therefore, rely extensively on the available rainwater commonly harvested through their already existing rooftops because it is affordable and available during the rainy season. In addition, it has a reputation for being secure for drinking and other household uses. Accordingly, water quality monitoring is essential to gather data that will aid in water resource management in any nation or community [44]. There is therefore need to assess the effect of different rooftops on the quality of HRW in the study area for potable use.

2 Materials and methods

2.1 Description of the study area

The study was done in Umuahia located in the south eastern region of Nigeria (Fig. 1). Umuahia is the capital city of Abia state, Nigeria and it is situated near the rail line that connects Port Harcourt with Umuahia South and Enugu City with its northernmost point. It has a population of about 147,167 [45] and is located in Nigeria's tropical rainforest zone at latitude and longitude 5° 52′ 0″ N, 7° 49′ 0″ E, 148 m above sea level (asl). The total precipitation throughout the year in Umuahia hovers around 2153 mm with lowest in December (average of 15 mm). September has the most precipitation, with an average of 322 mm [46]. In terms of the temperature, the hottest months of the year are January February and March. The average high temperature is over 27 °C. Throughout the year, the average relative humidity is between 54 and 75.4% and reaches its highest level during the rainy season (usually from April to October). Umuahia city is an ancient calm city with several old buildings, but recently has started recording lots of anthropogenic activities. From the researchers observation during reconnaissance study, there are signs of rural–urban migration from neighboring security challenged states into Umuahia. This has resulted to the spring up of pockets of businesses which include manufacturing of small goods and services. Vehicular traffic flow has also increased with increased human population and little industrialization.

Fig. 1
figure 1

Map of Umuahia showing the study area

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2.2 Reconnaissance survey

The researchers undertook an initial investigation in the study area to identify households with different roof top types. With the help of associate engineer, four available rooftop types were identified purposively based on similarity in the duration of use (between 10 and 12 years) and accessibility of the catchment area namely; corrugated iron roofing sheets, asbestos roofing sheet, aluminum roofing sheet, and rooftops with Harvey tiles. The different roof types were coded in the following manner; Corrugated iron roofing sheets (COR3), Asbestos roofing sheet (ASR1), Aluminum roofing sheet (ALR2), and Harvey tiles roofing sheet (HTR4). In addition, a control sample which was taken directly from the atmosphere without allowing the rainwater touch any surface and it was coded as Atmospheric rain control (ARC5).

2.3 Collection of rain water samples

The researchers sampled a total of 12 households (made up of 3 replicates each of Harvey, corrugated iron, Aluminum and Asbestos roof top types) at different locations within the study area with roof top types of interest with common duration of use (10–12 years) in the study area. 15 samples were collected for each of onset rain, peak and cessation rain events and 45 samples for the entire study. One educated person was selected and trained in each of the households on how and when to collect the rainwater and phone numbers given to these selected persons for more information and communication. The educated persons were given specific instructions to collect rain water roof run off only during moderate to heavy rain events and should be collected after 15 min into the rain event with steady current of fall. This is to ensure that some of the dusts and debris would have been washed off from the roof tops prior to collection as it represents the typical ideal household practice during Rain Water Harvesting (RWH). Samples of roof top runoff rainwater were collected with the use of stainless-steel basins (5L) which were placed about 5 feet above ground level on wood-made stands. The Harvested Rainwater (HRW) from the basin were then flushed into neatly polythene packaged 1 L bottles, corked, and labeled with the various roof types codes as designated before being put in freezers with ice blocks. The samples were carefully selected to ensure a good representative of HRW. Containers for the samples were cleaned with sterile water and drained before collecting samples of rainwater from various roof types. The rainwater samples were collected during Onset Rain (April), peak rain (July) and cessation rain event (October) in the year, 2022.

2.4 Chemical analysis of harvested rainwater (HRW)

The HRW samples were analyzed for Chemical parameters viz; Hydrogen ion concentration (pH), Total Dissolved Solids (TDS), Electrical Conductivity (EC), Nitrate (NO3−), Sulphate (SO42−), and Chloride (Cl−).

The insitu HANNA pH meter (model HI 8424) was used to determine the pH of the HRW. It was calibrated with the use of buffer solutions 4.7 and 10. TDS was analyzed with the use of HACH 44600–00 Conductivity/TDS meter. The probe was inserted into the sample container and held there until a consistent measurement was obtained and recorded in mg/l. EC measurement was done at the sites of sampling to forestall alteration. The values of rainwater samples were determined using a Suntex 120 conductivity meter submerged in rainwater samples and expressed in umhos/cm = micromhos per centimeter (nS/cm) [47]. Phenol di sulphuric acid was used to determine NO3 by evaporating a known amount of HRW. Ammonia, distillation water, and phenol di sulphuric were added. Utilizing a spectrophotometer, the nitrate generated was quantified. The results were then stated in mg/l after the nitrate was quantified using a nitrate standard. In analyzing SO42−, 10 ml of conditioning reagent was added to 25 ml of samples of HRW, then 0.3 g of BaCl2 was added. Then, 100 ml of double-distilled water was added to the mixture to dilute it. Samples that had been prepared were left to stand for 45 min. The colorimeter at 440 nm was used to gauge the samples’ concentrations. The same wavelength was used to prepare and run a blank without BaCl2. Silver chloride’s turbidity in samples of rainwater was measured in order to determine the concentration of Cl−. By using a standard volumetric method, the concentration of (Cl-) was obtained [48]

2.5 Microbiological analysis of HRW

Prior to examination on a plate made of solidified nutrient agar and incubation at a temperature of 37 ℃ for 24 h, samples for microbiological analysis were maintained in a sterilized 500 ml plastic bottle with a cap to stop bacterial growth. Cultural, morphological, and biochemical examinations of the isolates were used to make the identification [49].

3 Results and discussion

From Table 1, the physicochemical parameters like pH in harvested rainwater (HRW) from roof top catchments during the month of April ranged between 6.20 and 6.75 across the different roof top catchments with an overall mean value of 6.5 (Table 1). Harvey tiles rooftops recorded less pH while asbestos recorded higher pH. The atmosphere had near neutrality in pH 6.90. The pH values of water samples recorded for all roof top types show that they are below the pH 6.5 – 8.5 WHO/ FMENV drinking water quality level and indicates acidity in harvested rainwater. According to WHO, [52] and [3], high acidity in drinking water has corrosive property and could adversely affect its taste and appearance. The pH result is slightly lower than 6.13–6.25 reported in Akure, Nigeria [53], 6.3–7.6 range reported in Krakow, Poland [49]. According to Ezemonye et al., acidic water can also help prevent bacteria growth [23]. The high acidity recorded in the area could be tied to the visibly seen pockets of anthropogenic industrialization that release acid anhydrides such as CO2, and SO2, and eventually fall as wet deposition within the area. This is evidenced by the deterioration of monuments, statues, structures and buildings which is one of the effects of acid rain [54]. Total dissolved solids ranged from 15.5 to 44.50 mg/l with asbestos roof having the highest value of 44.50 mg/l and Harvey tiles recording the least value of 15.50 mg/l with an overall mean of 25.70 mg/l, higher than the control value of 7.0 mg/l, but way lesser than the WHO/FMENV standard of 250-500 mg/l. The result is above the range values of TSS (0.01 – 0.08 mg/l) of onset rain obtained by Ezemonye et al. [23]. There was significant difference in TDS among the selected roof catchments at p ≥ 0.05 level. Electrical conductivity (EC) ranged between 27.50 and 66.00 μS/cm, with Harvey having the least and asbestos recording the highest value (66.00μS/cm), with overall mean value of 43.60 μS/cm, greater than control with 12.00 μS/cm. The EC recorded significant differences among the selected roof catchments at p ≥ 0.05 level. The harvested rain water (HRW) from the asbestos roof was near the 100 μS/cm limit for WHO which indicates a near limit dissolved levels of Na+ and Cl−(salinity) which makes the water potentially risky for consumption. The near permissible limit level recorded in asbestos could be as a result of the particulate pollution and deposition arising from the activities of pockets of industries within the study area which are into manufacturing of goods and services. According to United States Environmental Protection Agency, USEPA [54] human activity or disturbances tends to increase the number of dissolved solids entering waters, which causes the conductivity of the water to increase. These human disturbances include polluting activities leading to discharges of materials, emissions and deposition arising from urbanization, increasing human population and industrialization. This leads to an rise in waste water discharge into aquatic systems and the release of contaminants into the atmosphere [55, 56], hence deteriorating water quality in the study area.

Table 1 Physicochemical quality of collected rainwater from roof tops during onset rain
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Nitrate (NO3−) ranged between 0.11 and 2.55 mg/l with Harvey tiles having the lower value and asbestos roof recording the higher value by asbestos roof with overall mean of 0.72 mg/l ≥ the 0.05 mg/l as control and below the stipulated value 40/10 mg/l WHO/FMENV standards for drinking water. Sulphate (SO42−) ranged between 1.19–14.00 mg/l with the least value being Harvey tiles and the highest being asbestos with the mean value of 4.73 mg/l ≥ 0.51 mg/l as control below the 250/500 mg/l WHO/FMENV standard. SO42− recorded no significant difference between Harvey tile and the atmosphere, while significant difference existed among asbestos, aluminum and corrugated rooftops at p ≥ 0.05 level respectively. Chloride ranged between 5.95 to 13.97 mg/l with Harvey tiles being the lowest and asbestos with the highest value, with the mean value of 8.81 mg/l ≥ 3.86 mg/l as control below the 250 mg/l WHO/FMENV standard. Chloride concentration indicated significant difference among the selected catchments at p ≥ 0.05 level.

From Table 2, pH negatively correlated with TDS (r2: -1.0), EC (r2: -0.97), SO42− (r2: -0.92) and Cl−(r2: -0.99).. TDS was positively correlated with EC (r2: 0.98), SO42−(r2: 0.90) and Cl−( r2:0.98). EC positively correlated with Cl− (r2: 0.96), NO3− positively correlated with SO42− (r2: 0.973) and. SO42− positively correlated with Cl (r2: 0.95) at different levels of significant during the onset of the rain in April. The significant correlations that occurred among TDS and SO42−, Cl.−, and EC further buttresses the fact that presence of dissolved anions and their interactions with one another in rainwater led to the high conductivity value (66.00 μS/cm) as recorded in (Table 1) in the asbestos roof in the study area. This is because the increase in dissolved solutes/anions increases TDS value which also leads to increase in electrical conductivity of water [54] High electrical conductivity in water reduces the quality and health of water and hence makes water unfit for consumption [57]

Table 2 Correlation of physicochemical parameters of Harvest rainwater in the month of April
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Table 3 summarizes rainwater harvested from the different roof types during the mid-rain in the month of July. The mean of pH differed significantly (P ≤ 0.05) between ASR1, ALR2, and COR3, however the mean of HTR4 and control did not differ significantly (P ≥ 0.05). Similarly, the means of Acidity, TDS, EC and Cl− had no significant difference (P ≥ 0.05) between HTR4 and control. The result shows that pH ranged from 6.55 to 6.90 with ASR1 having the lowest value and HTR4 and control with the highest value, with a mean pH of 6.73 less than 6.90 of the atmospheric rain waters as control. The mean value of pH in rainwater from the selected rooftops in the present study is lower than pH < 4.9 recorded In Korea during most precipitation events [58,59,60]. Total dissolved Solids (TDS) ranged from 5.00 to 29.00 mg/l with control having the lowest value and ASR1 with the highest value, with a mean TDS of 16.6 mg/l less than 5.00 mg/l of the atmospheric rain water as control. Electrical Conductivity (EC) ranged from 9.00 to 43.50 µs/cm with control having the lowest value and ASR1 with the highest value, with a mean EC of 26.5 µS/cm less than 9.00 µs/cm of the atmospheric rain water as control. Nitrate (NO3−) ranged from 0.04 to 0.46 mg/l with control having the least value and ASR1 with the highest value, with a mean NO3− of 0.158 mg/l and 0 mg/l of the atmospheric rain water as control. Sulphate (SO42−) ranged from 0.11 to 3.30 mg/l with control having the 0 values and ASR1 with the highest value, with a mean SO42− of 0.694 mg/l and 0 mg/l of the atmospheric rain water as control. Chloride (Cl−) ranged from 0.83 to 4.98 mg/l with control having the lowest value and ASR1 with the highest value, with a mean Cl− of 2.536 mg/l less than 0.83 mg/l of the atmospheric rain water as control.

Table 3 Physiochemical quality of collected rainwater from roof tops during peak rain (July)
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Table 4. illustrates the Correlation between the Physiochemical Parameters of rainwater harvested during the month of July. From the table, pH negatively correlated with acidity (r2: 0.97), TDS (r2: 0.99) EC (r2: 0.99) and Cl– ( r2: -0.95) accordingly. TDS correlated with EC (r2: 1.00), NO3−(r2: 0.89), and Cl−(r2: 0.97). The sources of TDS and EC may come from atmosphere and human activities [61, 62]. EC positively correlated with Cl−(r2: 0.95). NO3− positively correlated with SO42− (r2: 0.92) and Cl−( r2: 0.97). According to Zhang et al. [63] correlations existed between Cl−, NO3−, and SO42− indicating CaCl2, that have a strong effect on acidity [64], and this could be attributed to the influence of the surrounding human activities in an urban environment.

Table 4 Correlation evaluation of physiochemical parameters of rainwater harvested in the month of July
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Table 5 summarizes rainwater harvested from the different roof types during the Late-rain in the month of October. The means of the Acidity, EC, TDS, NO3− and Cl− differed significantly across the different roofs (P ≤ 0.05). The means of pH differed significantly (P ≤ 0.05) between ASR1, ALR2, and COR3, however the means of HTR4 and control did not differ significantly (P ≥ 0.05). The result shows that pH ranged from 6.40 to 6.85 with ASR1 having the lowest value and HTR4 and control with the highest value, with a mean pH of 6.64 less than 6.85 of the atmospheric rain water as control. The pH values found in this study differed from those found in [65] and [66], who reported pH values for harvested rainwater ranging from 5.2 to 11.4. Total dissolved Solids (TDS) ranged from 7.00 mg/l to 37.05 mg/l with control having the lowest value and ASR1 with the highest value, with a mean TDS of 21.3 mg/l lower than 7.00 mg/l of the atmospheric rain water as control. Electrical Conductivity (EC) ranged from 11.00 to 55.50 μS/cm−1 with control having the lowest value and ASR1 with the highest value, with a mean EC of 31.6 µS/cm lower than 11.00 µS/cm of the atmospheric rain water as control. The EC value found in this investigation was similar to that reported by [67], who noted a range of 18 to 61 S µS/cm. Nitrate (NO3−) ranged from 0.04 mg/l to 1.24 mg/l with control having the lowest value and ASR1 with the highest value, with a mean NO3− of 0.384 mg/l lower than 0.04 mg/l of the atmospheric rain water as control. Sulphate (SO42−) ranged from 0.08 mg/l to 6.58 mg/l with control having the lowest value and ASR1 with the highest value, with a mean SO42− of 1.97 mg/l less than 0.08 mg/l of the atmospheric rain water as control. Chloride (Cl−) ranged from 1.35 mg/l to 9.51 mg/l with control having the lowest value and ASR1 with the highest value, with a mean Cl− of 1.35 mg/l less than 4.52 mg/l of the atmospheric rain water as control. The rainwater runoff from all the roof types in the month of July all met the WHO [68] standard of 250 mg/l for drinking water. This is in line with [69], who reported rainwater harvested from thatch, aluminium rooftop, asbestos, corrugated iron roofing sheets being permissible to WHO standards for drinking in Delta State.

Table 5 Physiochemical properties of cessation rain event (October) harvested from different roof types catchment
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During the month of October in Table 6, pH in rainwater recorded negative correlation with TDS (r2: 0.96), EC (r2:0.96) and CL- (r2:0.90), TDS positively correlated with EC (r2: 0.966), Cl- (r2: 0.965) and SO42- (r2:891). EC positively correlated with NO3-, SO42-, Cl- with r2: 0.892, r2:879, and r2:951 respectively at ≤ p 0.01 level. NO3- positively correlated with SO42-, Cl-, with r2: 0.990 and r2: 0.965, SO42- correlated with Cl- (r2: 0.98) at p≤ 0.05 level of significant respectively.

Table 6 Correlation evaluation of physiochemical parameters of rainwater harvested in the month of October
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Table 7 shows the temporal differences in rainwater collected during rain events in April, July, and October shows that chemical characteristics increased at the beginning of the rain, decreased in the middle of the rain, and increased again during the month of October that marked the end of the rain. (Fig. 2). The outcome is consistent with the findings by Ubuoh [70] in Akwa Ibom State, Ezemonye et al. [23] in Edo State of Nigeria and Förster [71]. According to [67], early rainfall events have the highest concentrations of contaminants in roof runoff when compared to subsequent rainfall events of the year. The present study of pH in rainwater from rooftops is at variant with the finding of [65, 67, 72], who observed that the pH levels in rainwater collected from different rooftops ranged from 6.73 to 8.92 for each of the three rain events.

Table 7 Temporal differences in collected rain water during the April, July and October rain events.’
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Fig.2
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Temporal variations of mean values of harvested rain quality

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From Table 8, Total Bacterial Load (TBL) ranged between 1.02 × 105 and 8.2 × 104 cfu/ml with lower concentration at Corrugated Iron (COR3) and higher concentration at Aluminum Rooftop (ALR2) with mean value of 6.6 × 104 cfu/ml greater than 5.8 × 104 cfu/ml of atmospheric rain as control. However, Total Bacterial Load: on the different rooftops was in the descending order of Aluminum Rooftop ≥ Harvey-Tiles Rooftop ≥ Asbestos Rooftop ≥ Corrugated Iron Rooftop, Total Coliform Count (TCC) ranged from 1.8 × 103 to 3.4 × 103, with ALR2 recording the least while ASR1 catchment recorded the highest value with the mean value of 2.6 × 103 with control having no growth. No growth was observed among the Salmonella Shigilla Agar (SSA), Thiocitrate Bile-salt Sucrose Agar (TCBS) and Eosin Methylene Blue Agar (EMB). The result is at variance with the observation of [23] that observed 13, 150, and 260Cfu/ml of TBC from Galvanized Iron, Aluminum rooftop and Asbestos rooftops respectively.

Table 8 Evaluation of the microbial contaminants in harvested rainwater in onset rain (April)
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Table 9 shows the result of the microbial load count of the rainwater harvested from the various roof types in July. From the result it was observed that TBL ranged between 4.2 to 9.6 × 103 cfu/ml with Harvey-Tiles Roof (HTR4) having the least concentration and Asbestos Rooftop (ASR1) with the mean value of 6.1 × 103 cfu/ml greater than atmosphere as control (4.2 × 103 cfu/ml). However, SSA, TCC, TCBS and EMB recorded none respectively. Microbial concentrations on rooftops were in descending abundance of: Asbestos Rooftop (ASR1) ≥ Corrugated Iron Rooftop (COR3) ≥ Aluminum Rooftop (ALR2) ≥ Harvey-Tiles Rooftop (HTR4).

Table 9 Evaluation of the microbial contaminants in harvested rainwater in peak rain event (July)
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Table 10 shows the result of the Total Bacterial Load (TBL) in rainwater from the various roof types in October that ranged between 1.08 × 103 to 7.8 × 104, with ASR1(Asbestos) recording the lowest bacteria load across while COR3 (Iron) had the highest bacteria load, with the mean value of 5.1 × 104 higher than atmosphere as control (5.1 × 104). Accordingly, no growth was observed among the Salmonella Shigilla species. Similarly, there was also no growth observed in the Thiocitrate Bile-salt Sucrose. TCC recorded 2.4 × 103 with only Asbestos Rooftop having the concentration while the rest recorded none. The abundance of TBL was in descending order of COR3 ≥ ALR2 ≥ HTR4 ≥ ASR1. There should be 0% CFU/100 mL of enterococci and E. coli. The World Health Organization (WHO) classifies the public health risk for E. coli counts in drinking water in the order of 0 cfu/100 ml (conformity), 1–10 cfu/100 ml (low risk), 10-100 cfu/100 ml (intermediate risk), 100-1000 cfu/100 ml (high risk), and above 1000 cfu/100 ml (very high risk) [73, 74]. The presence of E.coli in drinking water, therefore, implies the water is unfit for drinking. They are therefore a significant indicator of fecal contamination [75]. The World Health Organization (WHO) advises that in 95 percent of samples taken from a specific water source, the total coliforms numbers for drinking water should be lower than 10 CFU/100 mL [76]. Additional treatment should be carried out before drinking if the total coliform counts are greater than 20 CFU/100 mL of water. The present findings showed that airborne microbes significantly contributed to the bacterial load of roof water at the study location. Strzebonska et al.[49] reported similar observation from harvested rainwater in Poland. The detection of Coliform in rainwater harvested from Asbestos roof type, corrugated iron sheet roof type and Aluminum roof type in April and Asbestos roof type in October is an indication that the rainwater is contaminated. This is in tandem with the finding of [77] who observed coliform as bacterial indicator from Asbestos roof type. This arises from the deposition by birds, small mammals and air borne micro-organisms [14, 67, 78, 79].

Table 10 Evaluation of the microbial contaminants in harvested rainwater in cessation rain event (October)
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Table 11 shows the organisms isolated from the harvested rainwater from roof types. This includes Enterobacter sp., Staphylococcus aurous, Streptococcus Sp., Bacillus Sp. and Escherichiacoli. The presence of these detected organisms in the rainwater samples collected from the selected roof catchments is an indication that the harvested rain water are of poor quality due to the sanitary status of the roofs. This is in relation with the finding of [23], that reported the poor sanitary state of roofs in Edo State In Nigeria.

Table 11 Colonial Morphological and Biochemical characteristics of the Isolates
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Table 12 illustrates the isolated bacterial species from roof types. Esherichia coli, Staphylococcus aurous, Bacillus Sp. and Salmonella Sp were the major organisms isolated. The control (c) had the lowest population of isolated organism, the least was in the month of April where Bacillus Sp was the only isolated organism. In July and October Bacillus Sp were isolated with Staphylococcus aurous. In April COR3 had Enterobacter Sp, Staphylococcus aurous, Salmonella Sp as isolated organisms. From the result, microbial concentrations dominated the selected roof catchments as well as rainwater harvested directly from the atmosphere as control.

Table 12 Distribution of the isolated Bacterial Species across the roof types samples
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Salmonella spp, Shigella spp and Vibro sp were detected in the harvested rainwater samples from corrugated rooftop which could lead to an outbreak of gastroenteritis. The result is consistent with the finding of [80] who reported human health risk associated with Salmonella leading to gastroenteritis outbreak that occurred in Trinidad, West Indies as a result of drinking contaminated rainwater. Uba and Aghogho [81] reported the presence of these pathogenic bacteria (Salmonella spp. Shigella spp and Vibrio spp) in harvested rainwater in River State of Nigeria. Escherichia Coli, Streptococcus Sp, Staphylococcus Sp, Bacillus Sp and Enterobacter Sp were isolated from the water samples harvested. Bacillus Sp is carried in dust particles and could be deposited on rooftops. Birds and other small mammals could be the source of other contaminants including Bacillus Sp [75].

4 Conclusion

The mean concentration of the physicochemical parameters of harvested rainwater were highest in April, reduced in July and built up again in October reflecting the temporal variation and the effect of rainfall intensity. This means that at peak rainfall (July), the mean concentration of the physicochemical parameters are consistently diluted. TBL (Total bacteria load) was found in all the rooftops, Total Coliform Count (TCC) was found only on asbestos roof type and Aluminum roof type respectively in April < the concentration of TBL in rainwater from the four rooftops in July and greater than TBL and TCC during October rain event. This indicates that TBL is the dominant microbe in rainwater followed by TCC in the four selected rooftops and were above the WHO limits of 1000 cfu/ml which is an evidence of contamination of harvested rainwater and is thus of very high public health risk if consumed without treatment. EnterobacterSp., Staphylococcus aurous, Streptococcus Sp., Bacillus Sp. and Escherichiacoli were organisms found in rainwater from the four roof types. From the results none of the roofing sheet emerged as the best in terms of the quality of the harvested rainwater during the rain events. Meanwhile, positively loaded physicochemical parameters in harvested rainwater were suspected to have originated from the atmosphere accumulated on rooftops due to human activities in the urban environment. The results showed that rainwater harvested from Asbestos rooftop had the highest level of contaminants followed by galvanized and Aluminum, while Harvey tiles roof type had the least contaminants, and highly recommended in building designs as it showed to be the safest roof catchment system for harvesting rainwater. Based on the results, rainwater harvested from rooftops should be boiled alongside the application of chlorine to remove all biological contaminants. Regular inspection and cleaning of rooftops, gutters, filters and rainwater storage systems will reduce the likelihood of contamination. Above all, human activities that can pollute the atmosphere should be checkmated by appropriate authority like State Ministry of Environment.