Drinking water in hot weather and during exercise
The daily references for water assume mild temperatures and moderate activity. In heat, or during long physical activity, the body loses more water through sweat, and the amount it needs can rise well above those figures.
What official sources say
- The NHS lists being in a hot environment and being physically active for long periods among the reasons you may need to drink more fluids.
- The National Academies note that people who are very active or live in hot climates may need more total water, and that heat exposure and high activity can lead to temporarily drinking too little.
- In heat waves, the CDC advises drinking more fluids than usual, not waiting until you are thirsty, and avoiding alcohol and very sugary drinks.
There is no single amount that fits everyone in the heat. It depends on the temperature, how hard you work, how long, your body and your health.
Signs you may need to drink
The NHS describes signs of dehydration that include feeling thirsty, dark yellow, strong-smelling pee, feeling dizzy or lightheaded, feeling tired, a dry mouth and peeing less often. Pale yellow pee is a useful everyday check.
More is not always better
Drinking very large amounts in a short time, especially during long endurance events, can lower the sodium in your blood, which is dangerous. Drink steadily rather than forcing large volumes. If you have a heart or kidney condition, or a doctor has limited your fluids, follow their advice instead.
Get help for heat illness
Heat exhaustion and heat stroke are medical problems, not hydration targets. If someone in the heat is confused, stops sweating, faints or has a very high temperature, call your local emergency number.
Using Water Tracker on hot days
Water Tracker does not raise your goal for the weather — it does not know it. On a hot or active day you can change your goal or log more freely, and the reminders keep their rhythm while you are awake.
Sources
- NHS. Water, drinks and your health.
- NHS. Dehydration.
- National Academies (2004). Report sets dietary intake levels for water, salt, and potassium.
- CDC. Heat and Health.
General information with sources, not medical advice.