It’s easy to forget, but even the most chiseled, rock-solid athlete’s body is still mostly water—60 percent, to be exact. Among H2O’s many roles in the body: lubricating joints, delivering oxygen to muscles, keeping your synapses firing, flushing out waste, and controlling your core body temperature. If you’re not getting enough water? Think about how the effects of dehydration could slow you down.

Maybe now it makes a little more sense why staying hydrated is so important for athletes, particularly weekend warriors who may be balancing work, family, and other obligations along with their training, and neglect their fluid intake in the hustle and bustle, says Carissa Galloway, RD, a dietitian, and personal trainer.

The Effects of Dehydration

“When you’re dehydrated even two percent, it affects your performance,” Galloway says. That’s why it’s important to make sure your fluids are topped off well before the starting flag falls. “When your body isn’t well-hydrated, it’s like when your phone battery is low,” Galloway says. “You go into power saver mode, which is the opposite of what any competitive athlete wants.”

And once you start racing, or engaging in any other physical activity, you’ll compound the effects of dehydration by sweating out water and electrolytes, which are key for muscle contraction. That inhibits muscle function—including that of your largest, most vital muscle, your heart—and lead to cramps and early fatigue.

Galloway’s motto, ABH (always be hydrating) is a good one. Her specific guidelines will actually help ensure you’re never left high and dry.

How Much Hydration Do You Need?

Fluid needs can vary a lot from person to person, but Galloway recommends this trick to find your baseline: Divide your weight in half and aim for that many ounces per day, minimum. A 150-pound woman, for example, would want to drink at least 75 ounces daily.

What you need beyond that amount will depend on how strenuous your workout is, when you’re doing it, and whether you’re a naturally salty sweater or not (yup, this is a thing, and if you find white streaks or residue on your body after a sweat sesh, it’s probably you).

“If you do a gentle 30 minutes on the elliptical, you may not need much,” says Galloway. “But if you’re working out for more than 60 minutes, in 80-degree heat, that’s when you need electrolytes from a safety standpoint.”

Your best bet, she says, is to know how the effects of dehydration show up in your body: dark-colored or infrequent urination, feeling light-headed or clammy or getting goosebumps (water helps regulate your body temperature, remember).

When Do You Need to Hydrate?

In a word: constantly. You should hydrate before, during, and after strenuous activity, says Galloway.

Again, everyone’s different in terms of digestion and what they can handle, and you want to avoid anything sloshing around in your stomach during your workout. But drinking four to six ounces about 30 minutes beforehand will help ensure you’re fueled up.

If you’re taking part in an endurance event, or tend to lose a lot of fluids quickly, you’ll want to keep chugging an ounce or two every half hour or so to replenish what you’re losing.

And after you’re done, have a recovery beverage, ideally with some protein and carbs to give your muscles back some of what you depleted. FYI: While the recovery window for replacing lost nutrients used to be considered 30-60 minutes, newer research is showing it may last up to two hours.

How Do You Get Adequate Hydration?

Hydrating isn’t just about chugging gallons of water. You also need to replace electrolytes, important nutrients that water alone can’t replace once you sweat them out. These nutrients, including sodium, potassium, and calcium, help muscle contraction and recovery, says Galloway. A sports drink specially formulated to replace these nutrients is a great choice during and after exercise. She recommends BodyArmor Lyte, which has natural electrolytes from coconut water and only three grams of sugar per serving.

Post-workout, you’ll want some protein, which helps rebuild muscle tissue in addition to replenishing your stores of carbs. Chocolate milk has long been touted for this purpose, but any protein-based drink is decent (though maybe not as tasty).

As for other edible products that claim to boost hydration, like goos and chews (gels and energy blocks), Galloway points out that you still need to take them with water to transport the nutrients to your body.

If you experience any of the signs of dehydration, it’s important to cut back your effort level until you can replace those fluids. After all, says Galloway, the most important thing isn’t to finish the race, but to finish the race safely.