The standard recommendation is about 35 ml per kg of body weight. A 75 kg person should drink approximately 2.6 liters daily as a baseline. Adjust upward for exercise, hot weather, and high altitude. This includes all fluid intake, not just plain water.

The '8 glasses a day' or '2 liters' rule is a rough guideline that works for smaller, sedentary adults but underestimates needs for larger or active people. A weight-based calculation is more accurate. A 90 kg active person needs over 3 liters, significantly more than the generic 2-liter recommendation.

Use a water bottle with ml markings and refill it a set number of times daily. Most standard water bottles are 500 ml or 750 ml. If your target is 2,500 ml, that is five 500 ml bottles or about three 750 ml bottles throughout the day.