Once on a hot day in Subic Bay, in the Philippines, Brett Sutton was on the pool deck coaching his elite athletes through a 90-minute swim session. This was during the era he was coaching Chrissie Wellington, and my visit was just a few months after she had won her first Hawaii Ironman. She was in the pool that day along with names like Nicola Spirig, Belinda Granger and Mariana Ohata.

Long before Sutton started coaching triathlon he was a national-level swim coach for Australia, a fact he referenced when he noticed that one of his pros had a 20-ounce water bottle perched above her lane on the deck. The triathletes were plowing through a long interval when Sutton spotted the bottle, picked it up and hurled it into a baby pool about 20 feet away. When the interval was finished, he told the perplexed athlete that the day he’d allow water bottles during swim workouts was the day they started having aid stations in Ironman swims. He later told me about his years of coaching Olympic-level swimmers, generally known to log thousands of meters per workout, 10 kilometers in a day not being overly weird, and taking water breaks just never happened. “And everyone was fine.”

Juxtapose that image with the staging of modern big-city marathons, where bountiful aid stations are placed every mile, and you can see the effect that guidelines by institutions like the American College of Sports Medicine (ACSM) and the Gatorade Sports Science Institute (GSSI) had during the 1990s.

GSSI guidelines promoted in 2002 included oft-heard advice like, “Drink early and drink often;” “Don’t wait until your thirsty;” and take in up to 56 ounces of fluid per hour. Stemming in part from the ACSM 1996 guidelines for hydration, the goal suggested for the runner or triathlete was to guzzle as much sport drink and water as you can tolerate guzzling. Tolerate being the operative word.

The chug-as-much-as-you-can-protocol has been diluted in recent years, so to speak. The current current ACSM guidelines encourage a level of moderation, urging athletes to drink no more than 32 ounces an hour while exercising or racing. The caution is to avoid “over-hydration” or “water intoxication,” also known as exercise-associated hyponatremia, which can result in “behavioral changes, confusion, drowsiness, nausea/vomiting, weight gain, muscle cramps, weakness/paralysis and risk of death.”

In the early 2000s, an outcome of discussions between two MDs, Dr. Tim Noakes and Dr. Lewis Maraham, the International Marathon Medical Directors Association (led by Maraham) adopted Noakes stand that the conclusions supporting drinking as much fluid as tolerable was dangerously skewed with by an incorrect reading of research data, and began setting up marathons to moderate fluid consumption rather than push it on each and every runner. Their guidelines advocated the following primary suggestions:

  1. Don’t drink water with the goal of drinking as much as you can tolerate.
  2. Rather, drink to quench your thirst, and less than 27 ounces per hour (800ml per hour).

To go down the rabbit hole on this, and it’s a deep one, read Noakes’s 428-page tome, Waterlogged: The Serious Problem of Overhydration in Endurance Sports (Human Kinetics). The entire history of hydration and sports drinks in endurance athletics and their connection to performance, health, and heat injury is laid out and worked through. A big takeaway is the idea that bypassing your sense of thirst, a super-complex mechanism developed through millions of years of survival-of the- fittest-evolution, has potential consequences that you don’t want to mess around with.

But what can you do? The most accessible and probably valuable strategy is to adhere to what many coaches suggest: Use your training sessions as your own personal lab. You are then applying a key fact in regards to the research science: You are accounting for individual variation. Based on the dangers of overhydration, less is generally better.

Will under-hydrating harm performance? Whatever the impact may be, the hard truth is this: The real danger to performance is under-training, not under-hydrating. If you’ve been a fan of endurance sports for a while, you may remember when Bob Kempainen—while leading the USA Olympic trials marathon out to qualify for the 1996 Olympics, TV cameras a few feet from his face—started barfing up sports drink in quartsize flurries. It freaked the network announcer out. Shouldn’t this guy hop in an ambulance? In fact, after throwing it all up at roughly the 21-mile mark, Kempainen sped up, opened up his lead, and won the race. The key was he was fit. If you haven’t done the work necessary to race a marathon or triathlon, the idea that hydration and fueling will save the day is like hoping to pay off credit card debt with a lottery ticket.

So number one, train hard and show up to your race fit. Two, dial it in the best you can. Dialing in perfect race hydration may be as simple as responding to your thirst. Or it may require substantial experimentation to find a rate of drinking that helps you feel as good as you can feel under the duress. You don’t bloat. You don’t puke. No melting down.

The low-hanging fruit when it comes to a smart and safe strategy is what you do when you’re not training. Mobility experts and physiotherapists suggest drinking half your weight in ounces per day (if you weigh 160, drink 80oz of water or even better water with electrolytes) to aid recovery and overall hydration and health. And healthy, supple muscles and connective tissues. Avoid the high-carb drinks for this. Rather, look to tabs and mixes like Hammer Endurolyte, SOS and Nuun. They add some zest to hydrating without an insulin-spiking blast of sugar.