How Much Hydration Do I need? A Practical Guide for Athletes

When did carrying around huge water bottles or the latest 40- or 48-ounce Stanley become a thing?

When did we start obsessing about drinking litres upon litres of water every day?

And if you’re an athlete, have you ever been more confused about electrolytes?

The hydration industry has done a brilliant job of making something relatively simple feel complicated.

So let’s strip it back.

How much hydration do you actually need?

The answer isn’t a number printed on a giant water bottle.

It depends on you, what you’re doing, how much fluid you’re losing and the environment you’re doing it in.

And for athletes, that can change dramatically from one day to the next.

Let’s start with the basics.

Why do we need water?

Water is essential to life.

It forms the basis of blood plasma, which transports nutrients, oxygen, hormones and other substances around the body. It helps remove waste products and provides the fluid environment needed for cells and tissues to perform.

It also plays a critical role in regulating   sweating and respiration.

When you exercise, particularly in warm or humid conditions, your body produces heat. Sweating is one of the ways your body gets rid of that heat.

As you lose fluid through sweat, your total body water and blood volume decrease.

If those losses become significant, meeting the demands of both your cardiovascular system and temperature regulation becomes more difficult. If you’re not drinking enough to support those demands, performance can suffer.

So yes, hydration matters.

But here’s where things get interesting.

How much water do you actually need?

There isn’t one magic amount of water that every person needs to drink every day.

Your fluid requirements are influenced by things such as:

• body size
• food intake
• physical activity
• temperature and humidity
• how much you sweat
• illness, particularly vomiting or diarrhoea
• altitude
• pregnancy and breastfeeding
• certain medications and medical conditions

That’s why telling everyone to drink two litres, three litres or some other arbitrary amount every day isn’t particularly helpful.

And it’s even less helpful for athletes.

Your hydration needs on a rest day in November are going to be very different from your needs six hours into an ultra-race in July.

So rather than asking:

“How much water should I drink every day?”

I’d rather you ask:

“How much fluid am I losing, and what do I need to replace?”

That’s a much more useful question.

How do I know if I’m hydrated?

Your body has a pretty sophisticated system for regulating hydration.

Thirst is one of the signals it uses to encourage you to drink. Your kidneys also interact with mechanical stretch receptors in your blood vessels, called baroreceptors, and adjust how much water you retain or excrete.

Urine colour can also give you a useful indication of hydration status.

Pale yellow urine is generally a reassuring sign.

But here’s an important point:

You don’t need crystal-clear urine to be hydrated.

In fact, if you’re constantly drinking large volumes of fluid in an attempt to keep your urine completely clear, you may simply be increasing your urine output rather than achieving some superior state of hydration.

This is one reason I don’t love the idea of forcing yourself to drink huge amounts of water just because someone told you that you should.

Can you drink too much?

Yes.

And this is particularly important for athletes.

Drinking excessive amounts of fluid, particularly during prolonged exercise, can dilute the concentration of sodium in the blood.

This is known as exercise-associated hyponatremia.

It can be serious and, in severe cases, life-threatening.

The important message isn’t that drinking water is dangerous.

It’s that more isn’t automatically better.

Hydration isn’t a competition to see who can drink the most.

Hydration for athletes is different

For athletes, particularly endurance athletes, the equation changes because you’re losing fluid through sweat.

And sweat loss can vary enormously between people.

Two athletes can ride the same route, at the same pace, on the same day and lose very different amounts of fluid.

Your sweat rate is influenced by your body size, exercise intensity, heat acclimation status, clothing, fitness and individual physiology.

That’s why a hydration strategy borrowed from someone else isn’t necessarily the right strategy for you.

Your sweat rate is useful information

One of the most useful things an endurance athlete can know is how their current fluid intake measures up to the actual fluid requirements of the training session.

You can gauge it relatively simply.

Weigh yourself immediately before a training session, ideally with minimal clothing and after using the toilet.

Record how much you drink during the session and note any urine you produce.

Then weigh yourself again afterwards, before replacing lost fluid.

Your change in body weight, alongside the amount you’ve drunk and any urine you’ve produced, can give you a useful estimate of how much fluid you’ve lost through sweat.

If you’re consistently finishing sessions with a large reduction in body weight (in my experience, anything over 4-5%) it’s worth looking more closely at your fluid intake and hydration strategy.

The aim isn’t necessarily to finish every session at exactly the same body weight. It’s about understanding your own fluid losses and using that information to make better decisions.

How much should I drink during exercise?

For shorter sessions in moderate conditions, you may not need to drink very much at all.

For longer endurance sessions, particularly in heat, your fluid needs will increase.

Your strategy should take into account:

• how long you’re exercising
• how hard you’re working
• the temperature and humidity
• your individual sweat rate
• how much fluid you can comfortably tolerate
• how much fluid is realistically available to you

The goal is to drink enough to support performance and health without either allowing excessive dehydration or drinking so much that you risk overhydration.

In my experience, this can range from 450ml per hour to 1.5 litres per hour. It really is context-dependent.

For longer events, hydration becomes a balancing act, which is why exploring your total body weight loss during training does provide useful and personalised information.

What about electrolytes?

This is where things can get particularly confusing.

Sweat contains electrolytes, including sodium.

The amount varies considerably between individuals, which is one reason why some athletes notice a much saltier sweat than others.

As exercise duration and sweat losses increase, replacing some of the sodium lost in sweat becomes increasingly important. Many sports products contain both carbohydrate and sodium.

Always check labels. It’s important to know how much sodium you’re getting. Many products deliver around 200-300mg sodium per 30 grams of carbohydrate.

Is this enough?

It depends on the factors we’ve talked about.

Some products are pure electrolyte products and may contain sodium, chloride, magnesium, calcium and potassium. If you’re an athlete, sodium is the most important electrolyte when it comes to replacing sweat losses.

Pure electrolyte products can deliver anywhere from 300-1000mg of sodium per recommended serving.

Bottom line – your electrolyte requirements depend on the situation.

A 45-minute winter training ride is very different from a 12-hour ultra in summer or a multi-day event.

So before reaching for the biggest electrolyte dose you can find, consider what you’re actually trying to replace.

What should I drink when I’ve lost a lot of fluid?

There are situations where it’s necessary to replace fluid and electrolytes quickly.

Long endurance exercise in hot weather is one. Illness involving vomiting or diarrhoea is another.

If you’re significantly dehydrated, an oral rehydration solution can be useful because it contains a carefully balanced combination of glucose and electrolytes designed to promote fluid absorption in the intestine.

The combination of glucose and sodium, transported together via sodium-glucose cotransporters, promotes absorption of fluid across the intestine, helping replace lost water and electrolytes.

If someone is significantly dehydrated because of illness, particularly if they’re unable to keep fluids down, medical advice may be needed.

A few simple hydration rules

If you want to take the noise out of hydration, I’d start here:

1. Don’t force yourself to drink a fixed amount just because someone told you to.

Your fluid needs aren’t identical every day.

2. Use thirst and urine colour as useful everyday guides.

You don’t need to keep your urine completely clear.

3. Pay attention to sweat losses during exercise.

If you’re an endurance athlete, knowing your approximate sweat rate can be incredibly useful.

4. Consider the conditions.

Heat, humidity, duration and exercise intensity all affect fluid requirements.

5. Think about sodium when sweat losses are significant.

Particularly during prolonged exercise or in hot conditions.

6. Don’t confuse hydration with fuelling.

Some carbohydrate products contain electrolytes, so when you drink, you’re getting both. Some hydration products contain electrolytes and no carbohydrates.

Know the difference and use accordingly.

7. Practise your hydration strategy.

Don’t wait until race day to discover that the amount you’re drinking makes your stomach feel like a washing machine.

Hydration doesn’t need to be complicated

So, how much hydration do you need?

Enough to support your body’s normal functions and replace an appropriate proportion of the fluid you’re losing.

Not a magic two litres.

Not a giant bottle because Instagram told you so.

And not an electrolyte sachet every time you leave the house.

For athletes, hydration becomes more individual as the demands increase.

The longer and harder you train, the more useful it becomes to understand your own sweat rate, the conditions you’re training in and how your body responds.

Hydration is about drinking appropriately.

And that’s a much more useful place to start.

 

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I’m Jill – If you’re interested in cutting through the marketing noise and getting practical, personal guidance on nutrition, fuelling and hydration, get in touch and let’s talk.

I work with both athletes and non-athletes.