Rapid Assessment of the Water Chemistry of Public Water Supply in Abeokuta , South-West Nigeria

The study examined the water supply situation in Abeokuta, with emphasis on the quality of water distributed by the Ogun State Water Corporation from the treatment plant of the Abeokuta Water Scheme. Water samples were collected from standpipes (taps) across the city randomly selected using the stratified random sampling method and was analysed for physical and chemical parameters: pH, total dissolved solids (TDS), electrical conductivity (EC), total alkalinity, total hardness, calcium, magnesium, potassium, sodium, nitrate, bicarbonate, sulphate and chloride. The result of the physical and chemical parameters was subjected to statistical analyses using the multivariate t-test. The result of the treated water was further compared with the result of the analyses of raw water obtained from the source of water used in the treatment plant. DOI: https://dx.doi.org/10.4314/jasem.v25i5.1 Copyright: Copyright © 2021 Odjegba et al. This is an open access article distributed under the Creative Commons Attribution License (CCL), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Dates: Received: 20 March 2021; Revised: 27 April 2021; Accepted: 07 May 2021

Increased rural-urban migration, conditioned by the quest for greener pastures has continuously stretched the barely sufficient urban amenitiesespecially water supply. In low-income countries particularly in Sub-Sharan Africa, residents in urban areas mostly result to self-supply and communal water supply systems as coping strategy (Hadipuro et al., 2013;Sutton and Butterworth, 2021). For instance, a World Health Organization 2019 report indicated that only 57% of the population in Sub-Sharan Africa had access to improved, fully functional, readily available, easily accessible and safe water supply (WHO, 2019). In the race towards SDG 2030, affordable, accessible and safe water is still a challenge (Ahmad, 2017). In Nigeria, water is still not accessible to a large percentage of the population in adequate quantity and quality. A 2020 joint report of Nigeria's Federal Ministry of Water Resources, National Bureau of Statistics and United Nations Children's Fund (UNICEF) indicates that 68% of the country's population lacks access to basic water supply service. The provision of water supply for public consumption and use in Nigeria is the constitutional responsibility of the Federal, State and Local Governments (Balogun and Redina, 2019).  ( Sadiq et al., 2020) (Akoteyon, 2019). Studies have also shown that water quality challenges have plagued public water systems (Akpor and Muchie, 2011, Odjegba et al., 2015, Balogun et al., 2017, Akoteyon, 2019. The focus of this study to assess the quality of public water supplied to Abeokuta city by the Ogun State Water Corporation and the effectiveness of the treatment process. Abeokuta is the capital of Ogun State. Public water supply is provided by the Ogun State Water Corporation through the Abeokuta Water Scheme. The source of water for the treatment plant at the Abeokuta Water Scheme is the Ogun River. Abeokuta city (Figure 1), lies between latitude 7 0 5' N and 7 0 20' N and longitude 3 0 17' E -3 0 20' E. It is easily accessible from Lagos, the industrial capital of Nigeria and the nation's major seaport.
The study area has a tropical climate, with distinct wet season (April-October) and dry season (November-March), and it is controlled by the prevailing southwest monsoon-wind reaching the land from the limit of Gulf of Guinea and the dry continental north -east wind (Harmattan) originating from the Sahara Desert. The wet season has two peak regimes, which are separated by the August break. The mean annual rainfall and temperature are about 1,270 mm and 28 0 C respectively while the estimated mean annual potential evaporation is 1,100 mm.

MATERIALS AND METHOD
The Rapid Assessment of Drinking Water Quality (RADWQ) was used (Ince et al., 2004). The sampling approach was used to select 40 sampling locations across Abeokuta city. Water samples were collected from public taps across the city. Water samples were analysed for physical and chemical parameters: pH, total dissolved solids (TDS), electrical conductivity (EC), total alkalinity, total hardness, calcium, magnesium, potassium, sodium, nitrate, bicarbonate, sulphate and chloride. The results of physical and chemical parameters for the tap water were compared with result of the analyses of raw water obtained from the source of water for treatment. This was done to ascertain the effectiveness of the water treatment process. Both results were further compared with the World Health Organisation (WHO), 2017 Guidelines for Drinking Water Quality. Result of the physical and chemical parameters was subjected to multivariate statistical analyses using ttest.

RESULTS AND DISCUSSION
The result of the physical and chemical parameters (Table 1) showed a pH range of 5.63 -7.44 with a mean of 6.91 ± 0.36. When compared with World Health Organisation (WHO) and Standards Organisation of Nigeria (SON) standards for drinking water quality (6.5 -8.5), the pH values for 11 samples were found to be below 6.5, an indication that the water is acidic. Diverse factors are responsible for low pH in drinking water. Dirisu et al. (2016) reports that carbon-dioxide and sodium carbonate create low pH. Dirisu et al. (2016) stated further that organic matter decomposition leads to the release of carbon dioxide which combines with water to form carbonic acid, a weak acid that leads to low pH. However, pH as a primary standard parameter has no health implication (WHO, 2017). The EC and TDS values ranged from 106 μS/cm -202 μS/cm with a mean of 132.10 ± 18.23 μS/cm, and between 53 mg/L and 101 mg/L with a mean of 66.07 ± 9.19 mg/L respectively. The range of values for EC and TDS fell within the SON acceptable limit of 1000 μS/cm and 500 mg/L respectively. EC is the measure of the capacity water to conduct electricity, while TDS is defined by the presence of inorganic salts and organic matter in water (Rusydi, 2018). EC has no direct human health impact, although, high concentrations could decrease the aesthetic value of water (Rahmanian et al., 2015) Elevated TDS concentration may result in laxative or constipation effects (Meride and Ayenew, 2016). Total alkalinity and total hardness had values ranging from 6 mg/L -30 mg/L with a mean of 8.34 ± 3.50 mg/L and 16 mg/L -66 mg/L with a mean of 43.39 ± 7.24 mg/L respectively and they both fell within the allowable limit of 150 mg/L set by SON and 100 mg/L by WHO respectively. Consumption of water with high hardness value can lead to gastrointestinal irritation (Alam et al., 2017). Alkalinity and hardness are collective used in predicting the corrosivity and scale formation of water in distribution networks (Boyd et al., 2016). The results of sodium indicated that it had values ranging from 2 mg/L -11 mg/L with a mean of 4.74 ± 2.13 mg/L, while that of Mg was between 6 mg/L -40 mg/L with a mean of 17.30 ± 6 mg/L respectively. Sodium ion values were below the maximum acceptable limit of 200 mg/L set by SON, while the values for magnesium were outrageously higher than the 0.2 mg/L and 0.4 mg/L set by SON and WHO respectively. Sodium is used for maintaining osmolarity, homeostasis and physiological functions in humans, though for hypertensive patients sodium concentration of 20 mg/L in water is recommended (Freije et al., 2019). Although it values were very high, magnesium is an essential element needed in good quantity by the human body (Chellan and Sadler, ODJEGBA, EE; BANKOLE, AO; SADIQ, AY; BUSARI, IO, I; LAYI-ADIGUN, BO 2015). The recommended dietary amount of magnesium is 6 mg/kg per day (Gröber et al., 2015). Therefore, for individuals with borderline magnesium deficiency, waterborne magnesium could make an important contribution to their total intake. A lack of magnesium leads to a decrease in the concentration of intracellular potassium and an increase in calcium levels (Cunha et al., 2012). Calcium values ranged from 10 mg/L -36 mg/L with a mean of 26.37 ± 4.80 mg/L while potassium values ranged from 0 mg/L -6 mg/L with a mean of 1.38 ± 0.83 mg/L. Calcium deficiency in humans can cause rickets, reduced blood clotting, while elevated calcium levels can lead to cardiovascular diseases (Meride and Ayenew, 2016). The low values recorded for K may be due to the fact that regular sources of K ions in surface and ground water are absent in piped water (Orewole et al., 2007); there is however, no healthbased drinking were standards for K (Ling et al., 2019;Arega, 2020). Results of anions indicated that bicarbonate was not detected in any of the water samples, while SO4 recorded a range of values between 1.17 mg/L and 378.39 mg/L with a mean of 253.87 ± 72.48 mg/L. However, they were below the WHO limits of 500 mg/L. High sulphate concentrations can cause scale formation and may be associated with a bitter taste in water that can have a laxative effect on humans and young livestock (Orewole et al., 2007). The high occurrence of sulphate is attributed to the Aluminium Sulphate (AlSO4) used as a coagulant in water treatment. Very low concentrations were recorded for nitrate, with values ranging from 0.01 mg/L -4.23 mg/L and a mean of 0.23 ± 0.55 mg/L. Chloride values ranged from 12 mg/L -43 mg/L with a mean of 16.53 ± 5.90 mg/L. Nitrate and Chloride ions recorded values within the acceptable limits of 50 mg/L and 250 mg/L respectively (WHO, 2017). The health implication associated with high concentrations of NO3, especially in young children, is the blue baby syndrome, which can cause death in the children (Meride and Ayenew, 2016).
Critical observation of the variation in the values of parameters analysed between the values obtained from the water sample collected at the water treatment plant and the various values obtained at the other sampling points, indicated 6 locations having pH values lower than that obtained at the treatment plant, which could be attributed to sulphur and amino acid compounds from human and animal excreta (Adekunle et al., 2007). Also, total hardness values were high at four locations; could be attributed to a variety of dissolved polyvalent metallic ions, predominantly calcium and magnesium cations. Three locations had potassium values higher that recorded at the treatment plant; however, K is important for human body functions like, blood pressure regulation and heart protection (Meride and Ayenew, 2016). Nitrate values for two locations were equally higher than that obtained at the water treatment plant. The major sources of nitrate pollution are domestic waste, industrial waste, sewage, sludge (Eddy and Ekop, 2007;Meride and Ayenew, 2016) which can only get into the distribution network through leaks in the pipes (Casillas et al., 2015). Chloride values higher than that obtained at the treatment plant is attributed to the presence increased electrolytes (Adekunle et al., 2007). The comparison between the result of raw and treated water is presented in Table 2. Seven out of the 13 parameters tested in the treated water were also tested in the raw water result. These include pH, EC, TDS, total hardness, calcium, magnesium, and chloride. The average raw water value for pH was 7.12, while that of treated water was 6.91. Raw water had an average EC value of 73.88 µS/cm while that of the treated water was 132.10 µS/cm. The result of total hardness indicated an average value of 19.93 mg/L for raw water, while that of treated water was 43.39 mg/L. The average raw water value for calcium indicated an average value of 14 mg/L, while that of treated water was 26.37 mg/L. The average raw water value for magnesium was 5.68 mg/L while that of treated water was 17.3 mg/L. The average raw water value for chloride was 31.25 mg/L while that of treated water was 16.53 mg/L. Except for pH, all the other six parameters (EC, TDS, total hardness, calcium, magnesium, and chloride) had their average raw water values lower than that of the treated water. The average pH value for the raw water at 7.12, which is almost neutral to alkaline, agrees with the report of Jaji et al. (2007). The fact that the average values for the other six parameters were higher for the treated water than the raw water can be attributed to the addition of water treatment chemicals such as calcium hypochlorite and aluminium chloride in the water treatment process. The result of the statistical analyses indicated that at p ≤ 0.05, the water samples is adjudged to have met the required Standards Organisation of Nigeria (SON)/WHO standards and is therefore fit for consumption.

Conclusion:
The study assessed the quality of the pipe distributed water supplied to Abeokuta city and the effectiveness of the water treatment process. Except for magnesium, all other parameters were within the acceptable limits of the water quality standards used. However, a drop in pH from the value obtained at the treatment plant while some other parameters experienced increment was observed. It is therefore imperative to note that these variations can only be due to the entrance of foreign matter into the distribution network at some point away from the treatment plant.