Key findings:

This research investigates the impact of temperature on the physicochemical properties of three popular sachet water brands in Ilisan-Remo, Nigeria. While most parameters met WHO standards, pH levels were aberrant at 44°C for all brands. This suggests that water vendors should avoid exposing sachet water to excessive sunlight to prevent pH levels from becoming acidic, which could pose health risks to consumers.

What is known and what is new?

Water quality is crucial for human health, both directly as drinking water and indirectly as a component of food. Temperature can influence the physicochemical properties of water and consequently affect microbial survival and growth, which is significant in food safety and other microbial environments. This research specifically examines the effect of temperature on the physicochemical properties of popular sachet water brands in Ilisan-Remo, Nigeria. While previous studies have investigated water quality parameters, this study focuses on the impact of temperature variation, particularly on pH levels. The findings suggest that at higher temperatures, pH levels of the sachet water brands deviated from WHO standards, indicating a potential health risk. 

What is the implication, and what should change now?

The implications of this research are significant for both consumers and sachet water vendors. The findings suggest that exposure to high temperatures can lead to a decrease in pH levels of sachet water, potentially rendering it unsafe for consumption according to WHO standards. Moving forward, sachet water vendors should avoid exposing their products to high temperatures, especially during storage and transportation. They should also ensure compliance with WHO standards for water quality, particularly regarding pH levels.

Water is an essential part of human nutrition, both directly as drinking water or indirectly as a constituent of food. Water remains the most important medium of illness and infant mortality in many developing countries, and even in technologically more advanced countries. It is also a key parameter influencing survival and growth of micro-organism in food and other microbial environment.

Water of adequate purity which is a life blood of our species, is of vital importance in the existence of human life [1]. The quest for cheap and readily available source of portable water has led to the emergence of sachet and bottled water in Nigeria and other West African countries. Packaged water is defined as any portable water processed and offered for sale in sealed food grade bottles or other appropriate containers for  human consumption (Nigerian food and drug administration control, 2002) [2] With the attendant increase in (sachet or bottled water) consumption, there has arisen a growing concern over the physico-chemical and bacteriological qualities of these products. Temperature is an important determinant of purity, since it influences physical, chemical and biological process, such as absorption of chemicals, chlorine decay etc (Monteiro et al., 2017) [3] and microbial growth and competition processes [4]. Several studies have been carried out on water quality of varying degree and coverage. These studies ranged from micro-biological to physico-chemical properties of water. For example, Alhassan et al., (2008) [5] analysed the physico-chemical properties of sachet water packaged in Kano metropolis. On the other hand, Obiri-Danso et al., (2003) [6] examined the microbiological quality of sachet drinking water and bottled water sold on the street of Kumasi, Ghana.

Not much work has been done or reported on the effect of temperature on the physico-chemical quality of sachet water sold in Nigeria especially at Ilisan Sagamu area of Ogun state, Nigeria. Therefore this work is meant to investigate the impact of temperature on the physico-chemical qualities of sachet water sold in this part of Nigeria considering the harsh temperature conditions that these sachet water are vended (very cold and very hot). The results of these investigations will add to knowledge in this area of our health care.

The three sachet water samples used in these investigation were collected randomly at Ilisan Remo Sagamu area of Ogun state, South western Nigeria, with the zip code of 121103 within the Latitude of 6.8932°E and Longitude 3.7105°N in the rain forest climatic region of the country. The study was carried out at Babcock University, Nigeria. The water samples were transferred into containers which were washed with ultra-pure distilled water, and were labelled and properly corked. They were placed in an ice chest at a constant temperature of 4°C to avoid changes in the quality integrity as a result of effects of light and temperature for the physico-chemical analyses of the water samples. The samples were stabilized in three specific temperature controlled conditions prior to analyses.

Other chemicals used in the determinations were of analytical grade. The equipments used in this study include: PHS-25 Model (pH meter)- search tech instruments, England, APHA 4500-B Model (Mohr’s Argentometric method)- search tech instrument, England, DDS-11A Model (conductivity meter)- search tech instruments, England, DHG-9030 A Model (TDS Oven)- search tech instrument, England, APHA 2540D (Gravimetric method)- search tech instruments, England,UV-VIS Spectrophotometer- 752N Model- search tech instruments, England, APHA 2340C (EDTA-Titrimetric method)- search tech instruments, England, APHA 4500-NO, (Colorimetrric method)- search tech instruments, England, Flame atomic absorption spectrometer (AAS)- search tech instruments, England.

The temperature conditions which were considered in the course of these investigations include: Room temperature (ambient) condition, 4°C and a sunlight activated temperature of 44°C.

Effect of temperature on ph

The pH of the water samples were measured using a pH meter PHS-25 Model (searchtech instruments, England). The value of each sample was taken after submerging the pH probe in three standard buffer solutions (pH 4.0, 7.0, and 10.0) and holding for a few minutes to achieve a stabilized reading. Subsequently, 20cm³ portions of each water samples were measured and probe was thoroughly rinsed with distilled water to avoid cross-contamination from other different samples. This was done for all the samples within the range of experimental consideration (ambient, 4°C and 44°C) respectively. All the investigations were carried out in triplicates and the mean values reported. These were done by electronically standard APHA 4500-H+ method.

Effect of temperature on conductivity

The conductivity of the water samples was determined electronically using a conductivity meter DDS-11A (searchtech instruments, England) using the standard method APHA 251B. The probe was calibrated using a 413µS/cm standard conductivity solution. The probe was submerged into the water sample and the reading was recorded after the disappearance of a stability indicator. After the measurement of each sample, the probe was rinsed with distilled waster to avoid cross contamination. The investigations were carried out in triplicates and the mean values reported at the various temperature ranges of ambient, 4°C and 44°C respectively. The results are recorded in µS/cm which were latter converted to ms/cm.

Effect of temperature on total dissolved solids (tds)

The test was carried out using gravimetric method (APHA 2540C). A portion of the filtered sample was measured into a pre-weighed foil dish. The whatsman filter paper of size 42 and space 125ml was used. The dish was dried in an oven DHG-9030 A model (searchtech instruments, England) at 105C. After drying, the oven temperature was rinsed to 180C for one hour and then re-weighed. The dissolved solid content of the sample was calculate from the difference in the two weights. TDS is reported in mg/L after calculations using the formula below:

TDS (mg/L) = (W1 - W2) / Sample volume (ml) 

W1= Weight of dried residue + dish

W2= Weight of empty dish

These determinations were carried out in triplicate and the mean values reported for all the samples at ambient, 4°C and 44°C respectively.

Effect of temperature on total suspended solids

Total suspended solids (TSS) was carried out using the gravimetric method (APHA 2540D). 1000cm³ of the sample was filtered through a pre-weighed filter paper (whatsman 42). the residue retained on the the paper was dried an oven (model DHG-9030A- searchtech instruments, England) between 103°C-105°C for one hour and transferred to a desiccator. The process was repeated twice to obtain constant weight. The total suspended solids were then calculated as the increase in the weight of the filter paper. TSS is reported in mg/L after calculations using the formula below:

TSS (mg/L) = (W1 - W2) X 100 / Sample volume (ml)

W1= Weight of dried residue + dish

W2= Weight of empty dish

These analyses were carried out in triplicates and the mean value reported at the various temperature ranges of consideration. 

Effect of temperature on chlorine

The chlorides in the water samples were determined titrimetrically using the Mohr’s Argentometric method as described in APHA 45000 - B (APHA, 2017) 100cm³ of the sample was measured into a conical flask. The pH of the sample was adjusted to 8 with 0.01M of sodium hydroxide 10cm³ of potassium chromate indicator was added to the solution to a pinkish yellow end point. A blank titration of 0.002cm³ was used for titration. The chloride content is reported in mg/L after calculations using the formula below.

Chloride in mg/L = Titre value X Molarity of silver nitrate X 35.45 X 1000 / Volume of the sample

These determinations were done in triplicates and the mean values reported.

Effect of temperature on sulphate

The sulphate concentration in the water sample was determined by the turbidimetric method (APHA 450 - SO4 ^2-) at 420nm wavelength using UV-VIS Spectrophotometer - 752N model (search tech instruments, England) 25cm³ of the sample was measured out which served as a blank during the reaction. Sulphate ion was precipitated in an acetic acid medium with barium chloride (BaCl₂) to form barium sulphate (BaSO₄) suspension which was measured and its equivalent sulphate ion was calculated from the equation of the calibration sulphate curve. A blank to which BaCl₂ is not added was analyzed along with the sample during analysis. All were carried out in triplicates and the mean values reported for all the three temperature considerations.

Effect of temperature on hardness

Total hardness in the water samples were determined by EDTA- Titrimetric method (APHA 2340C). The water sample was thoroughly shaken and 25cm³ was taken and diluted to 50cm³ with distilled water and 2cm³ of phosphate buffer solution was added to bring the pH of the water sample to 10. Three drops of eriochrome black T indicator was added. This was titrated with 0.01M EDTA to a blue color end point. Hardness was then calculated as:

Hardness (EDTA) as mg CaCO₃/L = A X B X 1000 / Volume of sample (ml)

Where, A = mL titration for sample

B = mg CaCO₃ equivalent to 1.00ml EDTA titrant 

The assessment was done in triplicates and the mean values reported.

Effect of temperature on nitrate

The nitrate in the water samples were determined by colorimetric method (APHA 4500 - N0₃). Brucine method was used for the nitrate determination in the samples. The reaction between nitrate and brucine usually produces a yellow color that is proportional to the nitrate concentration and this was measured at 410nm using a UV-VIS Spectrophotometer - 752 N Model (search tech instruments, England). Nitrate ion was calculated from the equation of the calibration nitrate curve. A blank was run along with sample during the analyses. These analyses were done in triplicates and the mean values reported.

Effect of temperature on total alkalinity

The total alkalinity of the water samples was determined by titimetric method (APHA 2320 B) Alkalinity was measured by titrating 50cm³ of the sample against 0,02N sulphuric acid solution by adding 2.3 drops of methyl orange indicator to a golden yellow end point.

Alkalinity mg CaCO₃/ L = A X N X 50000 / Ml sample

Where A= Ml standard acid used

             N = normality of standard acid

These were done in triplicates and the mean values reported.

Effect of temperature on iron, magnesium and potassium 

The analyses of heavy and trace metals such as Fe, Mg and K were carried out based on standards approved by APHA using flame atomic absorption spectrometer (Varian spectrAIto, California, USA). For the analysis of Fe, Mg and K, direct extraction, air-acetylene flame method (APHA 3111B) was used. The calibration stock standard solution used was NIST traceable reference ACCU Standard (New Haven, USA) for each tested element was prepared according to its concentration and used to calibrate the system before analyzing each of the samples. The results were recorded automatically on a computer connected with the AAS system. The analyses were equally done in triplicates and the mean values reported. 

Table 1: Result of the Effect of Temperature on Ph

From the table above, it can be clearly seen that at 44°C, the pH of Haze and Babcock sachet water deviated much from the world health organization standard as indicated above. Though Kenny T also deviated from the standard but the level of deviation was not much as compared with Haze and Babcock sachet water. This indicates strongly that both Haze and Babcock sachet water should not be vended at elevated temperatures (high sunlight) situations.

At ambient temperature, there were some levels of deviation from the standard as shown in table 1. This implies that this sachet water should not be taken when hot. 

Similar observations have been made by other researchers (Monteiro et al., 2017) [3].

Table 2:  Result of the Effect of Temperature on Electrical Conductivity

From table 2, it can be seen that the electrical conductivity of these water samples fell within the acceptable range. However as indicated in the table, increase in temperature impacted positively on the conductivity of the water samples within the range of experimental consideration.

Table 3:  Result of the Effect of Temperature on Total Dissolved Solids (TDS)

As could be seen from the table above, the total dissolved solids within the range of experimental consideration fell within the WHO limit. Though, the values were high at elevated temperatures. This could be attributed to dissolving of the packaging materials which are low density polyethylene materials.

Table 4:  Result of the Effect of Temperature on Total Suspended Solids (TSS)

As shown from table 4 above, the total suspended solids for all the water samples analyses gave excellent results at all temperature ranges of experimental consideration.

Table 5: Result of the Effect of Temperature on Chloride

Table 5 above shows that the effect of temperature on the chloride content of the water samples fell within the acceptable limit. Equally, high temperature indicated a rise of the chloride content of the water samples within the range of experimental consideration.

Table 6:  Results of the Effect of Temperature on Sulphate

Table 6 above shows that temperature did not impact on the sulphate content of the water samples negatively. The values obtained fell within the acceptable standard.

Table 7:  Results of the Effect of Temperature on Total Hardness

Table 7 shows that the total hardness of the water samples fell within the acceptable standard. The trends of increment of the values with increase in temperature is also maintained.

Table 8:  Result on the Effect of Temperature on Nitrate

Table 8 above shows that the nitrate content of the samples fell within the acceptable standard.

Table 9:  Result on the Effect of Temperature on Phosphate

From the table above, it can be seen that at ambient temperature, the phosphate content of Haze sachet water is at the threshold of the limit. However, it normalized at 4°C and 44°C respectively. But the values obtained for Kenny T and Babcock sachet water fell within the limit at all temperature ranges of experimental considerations. 

Table 10: Results of the Effect of Temperature on Total Alkalinity

Table 10 above shows that the total alkalinity of the three water samples fell within the acceptable values. This implies that with respect to the measured variable, the water is good for consumption within the range of experimental considerations.

Table 11:  Result of the Effect of Temperature on Iron

From the table above, it can be clearly see that the iron content of the water samples fell within the acceptable standard within the regions of experimental considerations.

Apart from the major deviation in the area of pH, other variables considered in this research conformed to the world health organization standard. Therefore, as indicated from the research findings, Haze, Kenny T. And Babcock sachet water should not be vended when exposed to high sunlight (at high temperature) ranges. At this temperature, the pH of the water will move towards acidic region which may cause some health challenges.

Funding: No funding sources 

Conflict of interest: None declared

Ethical approval: The study was approved by the Institutional Ethics Committee of Babcock University

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2. NAFDAC (2002). Guidelines for registration and production of packaged water in Nigeria. Website: www.nafdac.org

3. Monteiro, Laura, et al. "Integrating water temperature in chlorine decay modelling: a case study." Urban Water Journal 14.10 (2017): 1097-1101. https://doi.org/10.1080/1573062X.2017.1363249

4. Prest, Emmanuelle I., et al. "Biological stability of drinking water: controlling factors, methods, and challenges." Frontiers in microbiology 7 (2016): 45. https://doi.org/10.3389/fmicb.2016.00045

5. Alhassan, A. J., A. A. Imam, and H. M. Yakasai. "Quality assessment of sachet water packaged around Kano Metropolis, Nigeria." Bayero Journal of Pure and Applied Sciences (2008): 83-87. https://www.ajol.info/index.php/bajopas/article/view/74162

6. Obiri‐Danso, K., A. Okore‐Hanson, and K. Jones. "The microbiological quality of drinking water sold on the streets in Kumasi, Ghana." Letters in Applied Microbiology 37.4 (2003): 334-339. https://doi.org/10.1046/j.1472-765X.2003.01403.x