A run in the sun has the potential to be a glorious, uplifting, and energizing experience, or, on the flip side, a nauseating, aggravating, sweaty grind.

For us, it’s normally the former, but we have foolishly made ourselves sick a handful of times (read: Lisa has made herself sick a handful of times) from dehydration. You might know the feeling: spotty vision, ringing ears, nausea. Dehydration is serious, y’all, so we asked Dr. Kristin Wootton, ND, to give us some advice for staying hydrated when running in the heat.

“When it all comes down to it, the biggest thing you can do to ensure you’re staying properly hydrated is to listen to your body,” says Wootton. And it makes sense. Coleman’s 6’7″ man body has completely different requirements for fluid intake than Lisa’s 5’11” female frame. And while body size and fitness intensity play a part in how water intake should be monitored, it’s about trial and error. “Test the different recommendations to see what works best for you,” Wootton says.

We know we’ll feel like garbage if we don’t stay hydrated, but why is it actually important?

Hydration during exercise is important in order to keep our blood plasma levels stable so oxygen and nutrients can be transported throughout our body (which is what keep us going). To determine your hydration needs during activity, weigh yourself before and after. The goal is to have your weight be roughly the same at both times–up to a two percent weight loss after a run is safe, but more than three percent can indicate that you’re dehydrated. If you notice weight gain after exercise, it may mean that you’re over-hydrating during your run. This can put you at risk for hyponaturemia, so you’ll want to do some trial and error to find your sweet spot for proper hydration.

What can we do pre-exercise to ensure we’ll stay hydrated on an hour-long run?

The best thing you can do beforehand is to stay hydrated throughout the whole day, everyday. Water makes up around two thirds of of the body, and is vitally important as it is involved in the functioning of our joints, detoxification pathways, digestion, etc.

…the biggest thing you can do to ensure you’re staying properly hydrated is to listen to your body.

If you’re a morning runner, drink one to two cups of water before you head out. This ensures that your body tissues can get a boost from the lack of fluid intake overnight. Alternatively, if you exercise in the evening, drink throughout the day, and increase water intake in the hours leading up to your run.

We’ve heard “Drink eight glasses of water per day” for decades. Is there really a magic number?

Eight to ten glasses of water per day may work for some of us, but it’s definitely not the perfect amount for everyone. More recently, health professionals have challenged this number. Really, the ideal amount of water for an adult to consume each day depends on many factors, including weight, diet, and activity level.

When thinking about proper daily intake, it’s important to pay attention to two key things: your thirst level throughout the day, and the colour of your urine. Our bodies are good at giving us signs that tell us what it needs, and thirst is our body’s way of saying it needs more water. If you drink water every time we feel thirsty, chances are we will be able to keep our body properly hydrated. But you find you’re busy and running around all day, setting an alarm on your phone to stop and check-in with your body to see if you’re thirsty can be helpful.

In addition to that feeling of thirst, urine colour can indicate our hydration level, too. It’s ideal to have pale yellow to clear urine throughout the day. This ensures you’re maintaining good hydration status. If the colour is darker, it may mean you’re dehydrated. But keep in mind that some supplements and medications can change the colour of your urine.

Is there something other than water that keeps the body hydrated?

When it comes to straight hydration, water reigns supreme. But don’t forget that water is found in foods and other beverages you consume throughout the day as well. The Physician’s Committee for Responsible Medicine has classified many common fruits and vegetables including cucumbers, celery, tomatoes, spinach, berries and broccoli, as containing more than 90 percent water, so snacking on them throughout the day can be beneficial for general hydration.

If you’re going on a shorter run (less than an hour), you can really just focus on water intake before, during, and after. If you tend to go on longer runs (over an hour) consider your electrolyte levels as well. On long runs, especially in the heat, your body will sweat more and not only lose water, but also electrolytes that contribute to the body’s fluid balance—specifically high levels of sodium and lower levels of potassium, magnesium, and calcium are lost in sweat.

Supplementing your water with a carbohydrate-electrolyte solution (like eload or even coconut water) can help to maintain not only proper fluid balance, but also provide your body with fuel to keep you going for longer runs.

Kris, what are some obvious signs that you might be heading to Dehydration City?

Signs of mild to moderate dehydration include: dry mouth, fatigue, dry skin, headache, dizziness/lightheadedness, minimal dark yellow urine, cool dry skin, and muscle cramps.

Signs of severe serious dehydration (think, hospital serious) include: extreme thirst, confusion, low blood pressure, rapid heart and breathing rate, and fever. If you notice signs of dehydration, stop activity immediately and start replenishing your fluid and electrolyte stores.

Kristin Wootton is a Naturopathic Doctor. Join her network on Facebook, Twitter, and Instagram. She WILL make you smarter…and healthier.