Frequent intake of sugar-sweetened beverage (SSB) provides excess calories and added sugars and is linked to weight gain/obesity,¹ cardiovascular disease risk,² asthma,³ dental caries,⁴ poor academic achievement,⁵ and low diet quality⁶ in children. In contrast, drinking plain water (ie, tap, bottled, and unflavored sparkling water), especially when it is substituted for SSBs, may help with managing body weight and improve diet quality thereby reducing the risk for chronic conditions. Drinking water can also prevent dehydration, which is linked to poor cognitive function, constipation, and headache.⁷ For example, a previous study reported that water intake was positively associated with Healthy Eating Index-2010 total scores among US adolescents.⁶

Adolescents are the highest consumers of SSBs⁸ and commonly have infrequent plain water intake.⁹ According to the 2010 National Youth Physical Activity and Nutrition Study, almost 3 in 10 US high school students reported drinking plain water less than 1 time a day.⁹ A recent study using 2011 to 2016 National Health and Nutrition Examination Survey data reported that caloric intake from SSBs was significantly higher among adolescents aged 12 to 19 years who did not drink plain water (288.4 kcal/day) than those who did (155.4 kcal/day).¹⁰ While plain water can come from tap or bottle water, tap water is more environmentally responsive and less expensive than bottled water.

In order to develop and implement interventions to increase plain water intake among US adolescents, understanding the correlates associated with plain water intake is important. However, information on factors associated with plain water intake among US high school students is limited.⁹ Thus, we examined associations of demographics, academic grades, and behavioral factors with frequency of plain water intake among a nationally representative sample of US high school students.

Overall, 48.7% of students reported drinking plain water <3 times/day, and 24.6% drank plain water <1 time/day. Based on χ² tests, plain water intake was significantly associated with all characteristics except sex (Table 1). Based on the multivariable logistic regression model, factors significantly associated with infrequent plain water intake were age ≤15 years (aOR = 1.20, 95% CI = 1.05–1.37; vs age ≥17 years); earning mostly D/F grades (aOR = 1.37, 95% CI = 1.07–1.77; vs mostly A’s), consuming regular soda 1 to 6 times/week (aOR = 1.92, 95% CI = 1.67–2.20) or ≥1 time/day (aOR = 3.23, 95% CI = 2.65–3.94; vs 0 times/day), sports drinks 1–6 times/week (aOR = 1.30, 95% CI = 1.14–1.49; vs 0 times/day), milk <2 glasses/day (aOR= 1.51, 95% CI = 1.31–1.73), fruits <2 times/day (aOR = 1.92, 95% CI = 1.66–2.22), and vegetables <3 times/day (aOR = 2.42, 95% CI = 2.04–2.89); and being physically active ≥60 minutes/day on <5 days/week (aOR = 1.83, 95% CI = 1.60–2.08). Students with obesity had lower odds of infrequent plain water intake (aOR = 0.63, 95% CI = 0.53–0.74; vs underweight/normal weight students; Table 2).

In our study, about half of students reported drinking a bottle or glass of plain water less than 3 times/day during the past 7 days. Furthermore, about 1 in 4 students drank plain water less than once a day. This is similar to a study from 2010, which showed that 54% of US high school students drank plain water <3 times/day.⁹ We found that the odds of infrequent plain water intake were higher among students who were ≤15 years old, were physically inactive, had poor grades, and had poor dietary behaviors. Similar to our study findings, a previous study reported that younger age, poor dietary behaviors (eg, lower intake of milk, fruits, and vegetables and higher intake of SSBs and fast foods), and physical inactivity were associated with infrequent plain water intake among US high school students.⁹

Similar to a previous study,⁹ we found that students with obesity had 37% lower odds for infrequent plain water intake as compared to underweight/normal weight students. It is possible that students with obesity might try to decrease energy intake from beverages by substituting plain water for SSBs. A previous study showed that students who were trying to lose weight were less likely consume SSBs than those who were not trying to do anything about their weight.⁵

In this study, students who reported earning mostly D’s or F’s had 37% higher odds for infrequent plain water intake compared to those who earned mostly A’s. Although there is limited information on associations between water intake and academic performance among US high school students, a previous study reported that the prevalence of infrequent plain water intake (<1 glass/day) was higher among middle school students who earned mostly D’s or F’s than those who earned mostly A’s (46.4% vs 32.9%, respectively) in Florida.¹⁴ Because dehydration is associated with decreased cognitive function and headache and rehydration could improve adverse effects of dehydration on cognitive performance,⁷ drinking plain water may be a strategy to support better academic performance without adding calories to the diet.

This analysis includes a large, nationally representative sample with a relatively high response rate. However, this study is subject to limitations. First, associations are cross-sectional; thus, directionality or causality cannot be determined. Second, plain water intake is measured in frequency rather than volume. A previous study reported that plain water intake is moderately correlated (r = .49) between times per day as assessed by a frequency questionnaire and servings per day as assessed by multiple 24-hour dietary recalls, and the proportion of people consuming plain water daily was higher using a frequency questionnaire versus 24-hour dietary recall (70% for ≥1 time/day vs 59% for ≥1 serving/day) among US high school students.¹⁵ Third, this analysis is limited to plain drinking water and does not assess overall water consumption; adolescents could also be receiving hydration from other foods and beverages. Finally, data are collected from adolescents who attended schools and thus are not representative of all adolescents.

In conclusion, this study showed that about 1 in 2 US high school students reported drinking a bottle or glass of plain water less than 3 times a day during the past 7 days, and 1 in 4 drank this amount less than once a day. Factors significantly associated with infrequent plain water intake were younger age; poor academic grades; higher intake of regular soda and sports drinks; lower intake of milk, fruits, and vegetables; and physical inactivity. However, students with obesity were less likely to have infrequent plain water intake. These findings suggest the need for actions to increase water intake among adolescents as a substitution for SSBs to better support healthy lifestyles. Identifying ways to increase plain water intake during adolescence and ensuring schools provide access to free drinking water throughout the school day might be key steps.