Not all "extra fluids" have to be plain water. You can reach hydration goals through various sources: Diarrhoea Treatment Guidelines
Your body requires more hydration when it loses water faster than usual or when it needs support processing waste. Common scenarios include: Extra Fluids
Doctors often advise extra fluids during respiratory infections like colds, flu, or bronchitis to replace losses from fever and to help thin mucus. Not all "extra fluids" have to be plain water
Fluid needs increase to approximately 2.3 liters (10 cups) daily during pregnancy and 3.1 liters (13 cups) while breastfeeding to support the body's increased demands. Managing Fluid Intake Extra Fluids
Hot or humid weather increases perspiration, while high altitudes and dry indoor heat can accelerate moisture loss through the skin.