Define default preferences

[opatry]

In the domain layer, given a device Locale and user gender & weight, we should be able to compute default preferences.

• from locale, infer volume unit
• from gender & weight, formula for daily target
  • Men: about 3.7 liters or 124 oz.
  • Women: roughly 2.7 liters or 92 oz.

The Academy of Nutrition and Dietetics, which bases its recommendation on a person’s weight, suggests 30 to 35 milliliters of fluid a day per kilogram that a healthy adult weighs. Therefore, for a 150-pound (68.2 kg) individual, fluid needs would be 70 to 80 oz. (2.07 to 2.37 liters). Others suggest taking your body weight in pounds and multiplying it by ⅔ or dividing it by two. Both formulas supposedly give you the amount of water in ounces you should drink daily.

(– source)

The current guidelines for water intake according to the Institute of Medicine adequate intake standards (3.7 L/d for adult men and 2.7 L/d for adult women) are calculated independently of obesity status.

(– source)

ChatGPT

A commonly used formula to estimate daily water intake is:

Water (ml/day) = Body weight (kg) × factor

Where:
• Factor typically ranges from 30 to 40 ml/kg, depending on activity level, climate, etc.

Example:

For a 70 kg person:
• Minimum: 70 × 30 = 2100 ml/day
• Active/Hot weather: 70 × 40 = 2800 ml/day

Adjustments:
• Gender: Men often need more due to higher lean mass.
• Activity: Add 500–1000 ml/hour of exercise.
• Climate: Hot/humid = more water loss.
• Health conditions: May increase or decrease needs.

This formula gives total water from all sources (drinks + food). About 20–30% typically comes from food.

No single “official” formula, but this is widely used in clinical and athletic settings.

Regarding units per country

Region	Common Unit	Notes
Most of the world	Liters (L)	Standard SI unit (e.g., 2.5 L/day)
USA	Ounces (fl oz)	Often 64–128 oz/day (1.9–3.8 L)
USA (medical)	Milliliters (mL)	Used in clinical settings (e.g., 2500 mL/day)
General	Cups	1 cup ≈ 240 mL; used in informal recommendations

Maybe we could let user choose Cup as a unit and do the mL conversion under the hood?
What would that mean in terms of UI?