How Much Water Should You Drink When You Run?

MedlinePlus, the National Library of Medicine's consumer health site, gives no single daily drinking target: it says to drink when thirsty and with meals, and to drink more when it is hot or you are exercising. It also warns about the opposite problem, low blood sodium, which sweating can contribute to. Its pages on water, dehydration, and hyponatremia (reviewed in 2025) are summarized below.

1. Your daily water baseline

MedlinePlus explains that water makes up more than two-thirds of your body weight and that every cell and organ needs it. One of its jobs is directly relevant to running: water helps regulate body temperature through sweating.

On quantity, MedlinePlus cites the Dietary Reference Intake for water: 91 to 125 fluid ounces (2.7 to 3.7 liters) a day for adults. Two details matter:

• That is total water from food and drinks, not just what you drink from a glass. Soups, milk, tea, coffee, juice, and water-rich foods all count.
• Individual needs depend on sex, weight, age, activity level, and any medical conditions.

MedlinePlus adds that there is no specific recommendation for how much water you should drink, and that if you drink when you feel thirsty and have beverages with meals, you should get enough to stay hydrated. It also notes that alcohol does not add to your body's water, because it is a diuretic.

2. Signs you are getting dehydrated

Dehydration means your body does not have as much water as it needs. MedlinePlus lists sweating too much, for example from exercising in hot weather, as one cause. Its signs of mild to moderate dehydration:

• Thirst
• Dry or sticky mouth
• Not urinating much
• Darker yellow urine
• Dry, cool skin
• Headache
• Muscle cramps

Signs of severe dehydration include very dark or no urine, dizziness or lightheadedness, confusion, rapid heartbeat and breathing, and listlessness. MedlinePlus says to call 911 if someone loses consciousness, becomes confused, has a fever over 102°F (38.8°C), or shows signs of heatstroke such as a rapid pulse or rapid breathing.

For mild dehydration, MedlinePlus suggests sipping water or sucking on ice cubes, or drinking water or sports drinks that contain electrolytes. It specifically says not to take salt tablets, which can cause serious complications.

3. The opposite problem: too little sodium

It is possible to get the balance wrong in the other direction. Hyponatremia means the sodium level in your blood is lower than normal. MedlinePlus explains that when sodium outside the cells drops, water moves into the cells and they swell, and brain cells are especially sensitive to that swelling. In severe cases, it can be life-threatening.

MedlinePlus lists sweating among the causes. Its prevention advice for active people is specific: if you play sports or do other vigorous activity, drink fluids such as sports drinks that contain electrolytes to keep your sodium in a healthy range.

The practical lesson for runners: on long, sweaty efforts, plain water alone is not always the full answer.

4. A simple routine for new runners

MedlinePlus's prevention tip for dehydration is to drink plenty of fluids every day and drink more when the weather is hot or you are exercising. Built around that, a beginner routine might look like this:

Every day

• Drink when thirsty and have a beverage with meals, as MedlinePlus suggests.
• Check your urine color; darker yellow is an early sign you need more fluid.

Before a run

• Start by checking for the early signs above: thirst or darker yellow urine.

During long or hot runs

• Bring fluid, and for long, sweaty sessions consider a sports drink with electrolytes, in line with MedlinePlus's advice for vigorous activity.

After a run

• Keep drinking when thirsty and with meals; food and other drinks also count toward your total water.

5. Hot days need a plan

MedlinePlus names exercising in hot weather as an example of sweating too much, one of the main causes of dehydration. On hot days, decide before you leave where you will get water, and treat headache, dizziness, or confusion as reasons to stop.

6. Key takeaways

• The Dietary Reference Intake for total water is 2.7 to 3.7 liters a day for adults, from food and drinks combined.
• MedlinePlus says there is no specific drinking target; drink when thirsty and with meals, and more when hot or exercising.
• Darker urine, thirst, headache, and muscle cramps are early dehydration signs.
• Don't take salt tablets; use water or electrolyte sports drinks instead.
• For vigorous, sweaty sessions, MedlinePlus suggests fluids with electrolytes to help prevent low blood sodium.