Most adults need about 2 to 2.5 liters of water per day. For children and teens up to age 17, a general estimate is about 40 ml of water per kg of body weight per day.
The exact amount can vary from person to person. Weight, age, weather, health conditions, and physical activity can all affect how much water the body needs. People who exercise may need about 500 ml to 1 liter more water for each hour of activity, especially if they sweat a lot.
Water helps the body remove waste, support the immune system, control body temperature, prevent constipation, reduce the risk of kidney stones, and keep the skin hydrated. It is also not necessary to wait until you feel thirsty to drink water, since thirst can already be a sign that the body needs fluids. Read more about the benefits of drinking water throughout the day.
Drinking too much water can also be harmful, especially for people with kidney or heart failure. Anyone with these conditions should ask a doctor or registered dietitian how much water is safe for them each day.