The amount of water a person should drink daily varies based on factors like age, sex, activity level, climate, and health. Here are general guidelines supported by expert sources:

• For healthy adult men, the average recommended total daily water intake is about 13 to 15.5 cups (approximately 3 to 3.7 liters) from all beverages and foods

• For healthy adult women, the recommendation is about 9 to 11.5 cups (approximately 2.1 to 2.7 liters) daily from all sources

• Children and teenagers require less, with amounts increasing with age. For example, children 4–8 years old need about 5 cups, and teenagers 14–18 years old need 8–11 cups daily

• Pregnant women should aim for about 10 cups (2.4 liters), and breastfeeding women about 13 cups (3.1 liters) per day

• Men typically need about 3 liters (13 cups) of fluids daily, women about 2.1 liters (9 cups), with adjustments for physical activity and hot climates

• The UK NHS recommends 6 to 8 cups (1.9 liters) of fluids daily, including water from food and drinks, suitable for temperate climates

• A practical rule of thumb is to drink about half an ounce to one ounce of water per pound of body weight daily. For example, a 200-pound person would need 100 to 200 ounces (3 to 6 liters) of fluids per day

• Water needs increase with exercise, hot weather, pregnancy, breastfeeding, and certain health conditions

• Besides plain water, fluids from beverages like tea, coffee, milk, and water-rich foods such as fruits and vegetables contribute to hydration

In summary, while the classic "8 glasses a day" rule is a simple guideline, most adults need between 9 and 15 cups of fluids daily, adjusted for personal factors. Listening to thirst and monitoring urine color can also help maintain adequate hydration.