How it works
Clear assumptions, not a mystery number.
The drinking-water setting uses 3 litres per person per day. The UK Prepare campaign describes 2.5 to 3 litres as a minimum drinking-water range and says that 10 litres per person per day provides more comfort with basic cooking and hygiene.
Pet water is added separately because needs vary substantially. Add any extra water required for baby formula, medical equipment or a care plan separately.