Background: It is a common practice for distributors or trader at sales points leaving bottledrnwater to sunlight before being sold. The exposure of bottled water to sunlight facilitates thernformation of toxic substances such as chloroform, haloacetic and terephthalic acid; increasernconcentration of nitrite; reduce concentration of fluoride and increase turbidity level whichrnhas a public health importance. The study on the effect of sunlight exposure of bottled waterrnon its quality is limited in Ethiopia. rnObjective: To assess the effect of sunlight exposure on physicochemical parameters ofrnbottled water in Addis Ababa, EthiopiarnMethods: Experimental observational study design was employed to assess the effect ofrnsunlight exposure on phyisco-chemical parameters of the sampled bottled waters fromrnOctober 3-30/2020 in Addis Ababa, Ethiopia. Randomly selected bottled water were exposedrnto direct sunlight for 28 days and the physicochemical parameters of exposed and nonexposedrngroupsrnwerernanalysedrninrneveryrnsevenrndays.rnArndescriptivernanalysisrnwasrncarriedrnoutrntornrncomparernrnthe results against the World Health Organization, International Bottled WaterrnAssociation and our country standards, and the labelled value. Mean values forrnphysicochemical parameters of bottled water before and after exposure to direct sunlight wasrncompared using paired sample t-test and Wilcoxon signed rank test. rnResults: The experimental results showed that the values of pH, Frn- rn, Mgrn wererndecreased from 7.31 to 7.02; 0.20 to 0.15 mg/L, 0.486 to 0.365 mg/L and 3.95 to 3.52 mg/Lrnrespectively as sunlight exposure increased. Whereas the level of NOrn2rn-rn, TDS and turbidityrnwere increased with increasing sunlight exposure from 0.00 to 0.02 mg/L, 82.82 to 85.24rnmg/L and 0.00 to 0.57 NTU respectively. The rest parameters (EC, Clrn, and totalrnhardness) were numerically decreased or increased irrespective of sunlight exposure.rnStatistically significant difference was observed on pH, Frn-rn, NOrn2rn-rn, and turbidity levels betweenrnexposed and non-exposed group only. rnConclusion: Sunlight exposure has been shown to increase the value of turbidity, NOrn, andrnTDS and decrease the value of pH, Frn-rn, Mgrn2+ rnand NOrn3rn-rn but it has not exceeded thernrecommended standards except fluoride and turbidity. The increment or decrement ofrnchloride, EC, hardness and Carn2+rn were not associated with sunlight exposure, instead it mayrnindicates the formation of toxic substances. rnRecommendations: Proper handling and storage of bottled water have to be given attentionrnto be on the safest side even if exposure didn't exceed most of the permissible value (limit).