How much water should I drink when working out?

Drink when you're thirsty, and for sessions over about an hour, aim for roughly 4 to 8 ounces (120 to 240 ml) every 15 to 20 minutes. Have a glass or two of water in the couple of hours before you start. For a normal 45 to 60 minute workout, that's all you need.

There's no single perfect number. Sweat rate varies a lot from person to person and with heat, humidity and intensity.

Before, during and after

• Before: about 16 oz (500 ml) in the 2 hours leading up to it. If your urine is dark yellow, drink more.
• During: small sips as you go. You don't have to finish a bottle in a 30 minute session.
• After: replace what you lost over the next few hours with water and regular meals. A rough check is the scale. If you lost weight during a hard session, that's mostly water, and about 16 to 24 oz (500 to 700 ml) per pound lost is a common guideline.

When water alone isn't enough

If you're exercising hard for over an hour, in the heat, or sweating heavily, you lose sodium too. A salty snack or a drink with electrolytes helps then. For a short workout, you don't need a sports drink.

Don't overdo it

Drinking far more than you need can dilute your blood sodium, a condition called hyponatremia. It's rare, but it happens in long endurance events when people drink well beyond thirst. Drink to thirst and you'll be fine.

Hydration is the easy part of a long session; getting out the door is harder. Runs and rides synced from Apple Health count toward a daily match in League of Fitness, which can be the push to get the long one done.

Signs to take seriously

Headache, dizziness, confusion, vomiting, a very fast heartbeat or no longer sweating in the heat are signs of heat illness or dehydration. Stop, cool down and get medical help if they don't clear quickly. If you take medication that affects fluids or have kidney or heart problems, ask your doctor what's right for you.