Assessing the effect of sunlight exposure on physicochemical properties of bottled water in Addis Ababa, Ethiopia: An experimental observational study

Abstract

Bottled water is potable water that is manufactured, distributed, or offered for sale and intended for human consumption. However, bottled water retailers usually expose bottled water to direct sunlight at the point of sale, and store it for extended periods. Therefore, this study aimed to investigate the effects of sunlight exposure and storage time on the physicochemical properties of bottled water. An experimental observational study design was employed to assess the effect of direct sunlight exposure on selected physicochemical parameters in four water brands (40 samples for both control and exposed) for 28 days in Addis Ababa, Ethiopia. The study's average sunlight intensity and sunshine hours from 3 October to 30/2020 were 197.7 ± 31.8 W/M2 and 7. 3 ± 2. 7 h, respectively. The mean values of the physicochemical parameters of bottled water before and after exposure to sunlight were compared using a paired sample t-test and Wilcoxon signed-rank test with a significance level of 0.05. Approximately 80% of the analysed parameters did not match the labelled value of bottled water. This study showed that the values of pH, F-, and NO3− were decreased from 7.31 to 7.02; 0.20 to 0.15 mg/L, and 3.95 to 3.52 mg/L, respectively. Whereas the level of NO2−, TDS, and turbidity was increased with increasing sunlight exposure from 0.00 to 0.02 mg/L, 82.82 to 85.24 mg/L, and 0.00 to 0.57 NTU, respectively. Statistically significant differences in pH, F−, NO2−, and turbidity levels were found between the exposed and non-exposed groups of bottled water. Apart from the increase or decrease in chemical concentration after sunlight exposure, the physicochemical parameters of the exposed bottled waters were within the recommended standards, except for fluoride and turbidity. However, the fluoride concentration was below the recommended level in both exposed and unexposed samples, with a further reduction in sunlight-exposed bottled water samples. Therefore, regulators should ensure that bottled water is protected against long-term direct exposure to sunlight to provide safe water to consumers.