In hot weather (above 85°F/30°C), increase your water intake by 20-30% over your baseline. In very hot or humid conditions, you may need 50% more. A person normally needing 2.5 liters might need 3-3.75 liters in hot weather.

Watch for dark urine, headache, dizziness, dry mouth, fatigue, and decreased sweating despite heat exposure. More serious signs include rapid heartbeat, confusion, and nausea. If you experience these, move to shade, drink cool water, and seek medical attention if symptoms persist.

Yes, especially if sweating heavily. Sweat contains sodium, potassium, and other electrolytes that plain water does not replace. Add a pinch of salt to water, drink coconut water, or use electrolyte tablets to prevent hyponatremia during extended heat exposure.