Let's do the math (based on [1]): If I weigh 85 kg and measure 185 cm (BMI 24.8, right at the edge between normal and overweight), my body surface to wash is 2

Let's do the math (based on [1]): If I weigh 85 kg and measure 185 cm (BMI 24.8, right at the edge between normal and overweight), my body surface to wash is 2.09 m². Let's assume a 3-minute shower at 15 liters per minute, so 45 liters of water. So 21.53 liters per m². If my weight is 120 kg (140% of above) and I still measure 185 cm (between Obesity I and II), then my body surface to wash is 2.42 m², an increase of 0.33 m². Applying the same ratio as above, at 21.53 liters per m², I would need 52.11 liters of water (115% of above). So a weigh of 140% results in a water consumption of 115%. Qualitative argument is right, but the effect is not linear. [1] https://stats.areppim.com/glossaire/body_mass_def.htm https://stats.areppim.com/glossaire/body_mass_def.htm