Hydration Target Methodology

Inputs and outputs

Formula

drink_floor_l = adult male 3.0, adult female 2.2, teen male 2.6, teen female 1.8
weight_driven_l = weight_kg * 0.028
lean_mass_adjustment_l = clamp((lean_mass_kg - sex_reference_lean_mass) * 0.006, -0.08, 0.18)
size_adjusted_l = max(drink_floor_l, weight_driven_l + lean_mass_adjustment_l)
activity_bonus_l = sedentary 0, light 0.08, moderate 0.14, active 0.22, veryactive 0.30
exercise_bonus_l = clamp((zone2_minutes - 120) / 300, 0, 0.16)
water_l = round(clamp(size_adjusted_l + activity_bonus_l + exercise_bonus_l, female 1.9-3.1, male 2.2-3.6) * 10) / 10
summer_hydration_adjustment_l = never 0, outside_only 0.2, all_day 0.4, day_and_night 0.6
winter_hydration_adjustment_l = never 0, outside_only -0.1, all_day -0.2, day_and_night -0.4

Calculation steps

1. Start with a demographic drink-floor reference.
2. Compare it with a body-size estimate based on weight and lean mass.
3. Add small activity and exercise bonuses.
4. Clamp the final daily target to practical sex-specific bounds.
5. Store climate adjustments separately so they can be shown and reviewed.

Guardrails

• This is a drinking-water planning target, not a prescription for total water intake from all foods and beverages.
• Kidney disease, heart failure, diuretic use, pregnancy, endurance sport, fever, diarrhea, and fluid restrictions require clinical guidance.

Sources

• Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate National Academies Press