For optimum health and best performance: drink 32-39 ml of fluid per kg of body weight daily in addition to what you drink while training or racing. During exercise, drink 475-825 ml per hour.


What you need to know to stay in the flow.

Water is the most critical of all exercise fueling needs. It cools your body and transports nutrients. But many athletes have trouble gauging how much fluid to drink. Attempting to replace all of the ounces they’ve lost as sweat, they often over-hydrate—which can have harmful, and even fatal, consequences.

The fact is, you can finish a race or training session with up to 2% weight water loss and still be okay. Forget advice to “drink to replace” or “drink even when you’re not thirsty.” It’s just plain wrong. Here’s what every athlete needs to know about hydration for best performance and optimum health:

• Your body simply can’t absorb fluids at the same rate that it loses them. You lose about 1 liter (about 34 ounces) of fluid per hour during exercise, on average, and more than that in extreme heat and humidity. With acclimatization and training, you can reduce fluid loss by up to 50%. But you can’t replenish fluids at the same rate you lose them during the event.

• Drinking too much water during exercise will impede performance and could make you seriously ill. Dr. Tim Noakes collected data for 10 years from some 10,000 runners participating in the Comrades Marathon., an 84.33 kilometers ultra event. Noakes noted the prevalence of hyponatremia (low blood sodium) during ultramarathons and triathlons in runners who hydrated excessively. When blood sodium concentration becomes too dilute, you can develop severe cardiac symptoms leading to collapse. Lesser degrees of impairment occur frequently from excess fluid intake. Noakes believes an intake of 1 liter (33.8 ounces) of hypotonic (low-electrolyte) fluids per hour will likely cause water intoxication and dilutional hyponatremia.

• Research has shown the optimal water intake for an average athlete during exercise to be about one water bottle (500-750 ml) per hour - give or take a few ounces, depending on your size and the weather conditions. The goal with hydration during exercise is to support natural fluid stores by consuming the amount your body can process. Dr. Noakes’s research showed that endurance athletes who consumed 475-825 ml fluid ounces per hour typically replenished as much fluid as is efficiently possible. According to Ian Rogers, MD, the author of several scientific articles on the dangers of over-hydration for endurance athletes, about 475-825 m per hour will fulfill most athletes’ hydration requirements under most conditions. “Like most things in life, balance is the key,” says Dr. Rogers.

• Good hydration regimen starts before you even get moving. For regular daily (non-exercise) hydration needs, aim for a fluid intake of 32-39 ml fluid ounces per kg of your body weight. That amount can include coffee, tea, and other liquids, but preferably pure, clean water--and it’s in addition to the amount you drink during exercise.

Bottom line: By hydrating properly—taking in no more than 475-825 ml (or slightly more in rare circumstances) of fluids per hour, you’ll attain peak performance with less fatigue, bloating, and cramping. And you’ll feel better before, during, and after your workout or race.

Daily hydration: foundation for success

Adequate daily hydration will help you stay strong and healthy before, during, and after exercise. Aim for 32-39 ml of fluid per kg of body weight daily in addition to what you drink while training or racing. You can include coffee and tea in this amount, but make it mostly pure, clean water.

45 kg 1.440 - 1.755 ml

50 kg 1.600 - 1.950 ml

55 kg 1.760 - 2.145 ml

60 kg 1.920 - 2.340 ml

65 kg 2.080 - 2.535 ml

70 kg 2.240 - 2.730 ml

75 kg 2.400 - 2.925 ml

80 kg 2.560 - 3.120 ml

85 kg 2.720 - 3.315 ml

90 kg 2.880 - 3.510 ml

95 kg 3.040 - 3.705 ml

100 kg 3.200 - 3.900 ml


Hammer Nutrition water bottles hold 500-750 ml of fluid. Consuming about one bottle per hour is an easy way to keep hydration on track.

Use caffeine with caution. Although it has ergogenic benefits, it also acts as a diuretic, speeding depletion of fluids.

Drink cold fluids as much as possible during exercise. Your body absorbs them more rapidly. Use an insulated bottle or hydration pack.

During exercise, avoid simple sugar fuels. They require more fluids and electrolytes to digest.

If you finish an event weighing more than you started, you over-hydrated. If you dropped 3% or more, you’re dehydrated. A loss of 2% is acceptable.