Total water intake by kilogram of body weight: Analysis of the Australian 2011 to 2013 National Nutrition and Physical Activity Survey.

Aim: Water is critical for human survival, yet water intake equations may not reflect contemporary populations. This research aims to determine the total water intake of a representative Australian population, per kilogram of body weight (mL/kg) and stratified by age and sex.

Methods: A secondary analysis of the 2011 to 2013 National Nutrition and Physical Activity Survey (n = 10 146) was conducted. Dietary intake from food and beverages was assessed by a 24-hour recall, with respondent's weight objectively measured. Data were descriptively analysed, with multiple linear regressions used to identify the impact of demographic and physiologic factors on total water intake (mL/kg).

Results: The median (interquartile range) daily total water intake per kilogram of body weight for children (2-8 years), adolescents (9-18 years) and adults (19+ years) were 77.1 (57.4-100) mL/kg, 40.4 (29.3-53.4) mL/kg and 35.5 mL/kg (26.1-47.8), respectively. Increasing height and waist circumference were associated with reduced total water intake, with a change of -1.03 mL/kg (-1.43, -0.618) [coefficient (95% confidence interval)] in children for height and -0.448 mL/kg (-0.484, -0.412) in adults for waist circumference. Similarly, seasonality decreased intake, with greatest reductions in winter [adolescents: -4.11 mL/kg (-6.83, -1.40)]. In comparison, being male, living in rural areas and having a physical occupation were associated with greater intake, by 1.73 mL/kg (0.347, 3.10), 4.74 mL/kg (3.47, 6.00) and 2.82 (trade workers: 1.08, 4.59) in adults, respectively.

Conclusions: Total water intake (mL/kg) decreased with age in both sexes. The results highlight possibilities to incorporate other factors into water intake equations to improve their accuracy.