RESULTS
Literature search: We identified 1327 articles in our initial search. After exclusion of duplicate papers and those that did not meet the inclusion criteria, we identified 11 full-text articles of potentially relevant studies. After full-text review, we excluded an additional 4 articles for the following reasons: studies that enrolled patients with chronic renal diseases or hemodialysis patients, papers that were conducted on critically ill patients, one document that was conducted on children. Finally, seven cohort studies were included in the current systematic review and meta-analysis[5, 6, 14-16, 19, 20]. Four studies had reported effect sizes for all-cause mortality[6, 15, 19, 20] and 6 studies for CVD mortality[5, 6, 14-16, 20]. Of these publications, seven had reported effect sizes for total water[5, 6, 14-16, 19, 20] and four for drinking water[5, 16, 19, 20]. A flow diagram of study selection is shown in Figure 1 .
Characteristics of included studies: Characteristics of included prospective cohort studies are presented in Tables 1 . All included studies published between 2002 and 2018. Participants in these studies ranged from 1055 to 35362 people, with an age range between 18 and over 70 years. The duration of the follow up of the included cohort was between 6 and 19.1 years. In total 116816 participants were enrolled in the studies. Among the included studies, 3 studies were done in the USA[5, 6, 19], 2 in Australia[15, 20], and the rest in Japan[14] and Netherland[16]. In total 14754 patients died due to all-cause in the studies and 7611 deaths were due to CVD. One study was performed on women[20] and 4 studies[5, 14, 16, 19] were reported effect size for men and women separately. Out of the remaining studies, two[6, 15] reported effect sizes for both genders in combination. To assay fluid/water intake, all studies had used a food frequency questionnaire and 24h recall. All included studies applied record linkage for assessment of mortality as the outcome. All studies adjusted the associations for age. Most cohorts controlled for some conventional risk factors, including body mass index (n=5), smoking (n=5), and energy intake (n=3). Some others had also adjusted for alcohol consumption (n=2) and other dietary variables (n=2). Based on the ROBINS-E tool, two studies had a low-risk of bias in all components (Supplemental Table 2 ).