Drinking Water When Training: A Simple Hydration Plan

Most of us get hydration wrong when we’re active. We either forget to drink until we’re already parched, or we neck water like it’s going out of fashion, worried about drying out. The problem is, relying on thirst alone often means you’re already a bit dehydrated. And drinking loads "just in case" can actually be dangerous. To get it right you don’t need some mystical formula, you just need to understand a couple of real numbers, figure out what your own body does, and have a straightforward plan for before, during, and after you exercise.

This guide cuts through all the vague advice. It uses actual figures from the NHS and sports medicine to show you what’s what. You’re going to see how to do that easy weigh-in trick to find your sweat rate, why that single number beats any one-size-fits-all rule, and what to look out for if you’re getting dehydrated or, the one people don’t talk about as much, drinking too much. Nothing complicated here, just a workable system for your next run, gym session, or bike ride.

Your Everyday Baseline: How Much Fluid Do You Need?

Before we even get into training days, it’s useful to know where you’re starting from. The NHS Eatwell Guide says a healthy adult should try to get 6 to 8 cups or glasses of fluid a day. That’s roughly 1.2 to 1.5 litres. And it’s not just plain water that counts. Water, lower-fat milk, sugar-free drinks, and even your tea and coffee all contribute. So that morning brew is officially part of your hydration.

You’ll need more than that baseline amount if you’re active, if it’s hot out, if you’re pregnant or breastfeeding, or if you’re unwell. A really simple way to check you’re on track, and one the NHS recommends, is to make sure your urine is a clear, pale yellow. If it starts getting dark, that’s your body telling you to drink more. Think of it as your own built-in hydration gauge. Getting this everyday bit right means you’re not kicking off a workout already short on fluids.

The Pale Straw Test

Forget complex charts. Just have a look at the colour of your urine before you flush. Places like the Korey Stringer Institute and the NHS use a basic colour scale for this. If it’s pale straw or light yellow, you’re doing well. Dark yellow or amber means you need to get some fluids down you. Making this a quick pre-training check takes no time at all and gives you a real sense of where you are before you start moving.

The Actual Numbers for Drinking Water During Training

This is where the general advice stops being very useful. The American College of Sports Medicine (ACSM), in their Position Stand on Exercise and Fluid Replacement, says 0.4 to 0.8 litres per hour is optimal when you’re doing intense endurance work. The top end of that is for quicker, heavier people in warmer conditions; the lower end suits lighter, slower efforts or cooler weather. For a more regular rhythm, guidance from the Korey Stringer Institute points to having about 200–300ml every quarter of an hour while you’re exercising.

Before you even start, the ACSM suggests drinking around 500ml a couple of hours before exercise. That 2-hour window is important—it gives your body the time to get rid of what it doesn’t need, so you don’t begin with a belly full of water sloshing around. The main idea from both ACSM and the National Athletic Trainers' Association (NATA) is to start drinking early and keep doing it at set times, not just when you feel parched, and to try and replace what you’re losing through sweat.

Why One Size Doesn't Fit All: Finding Your Sweat Rate

Here’s the bit that’s actually useful: those numbers above are just guidelines. Your own personal sweat rate is the thing that really counts. The Korey Stringer Institute points out that sweat rates vary massively between people—from about one litre an hour all the way up to maybe three litres an hour. It depends on how used to heat you are, your fitness, what you’re wearing, and the conditions. This is why a single fixed amount can’t possibly work for everybody.

The only way to know your own number is to measure it. And it’s dead simple. Weigh yourself in as little clothing as you can before a session, then again straight after, making sure you towel-dry first. Every 1kg you lose is roughly equivalent to one litre of sweat. You then add back anything you drank during the session to work out your true hourly rate. Say you were 75kg before, 74kg after, and you drank 500ml during a one-hour run. You lost 1kg plus the 0.5kg you took in, so your sweat rate was 1.5 litres per hour. Do this test in the summer and then again in winter; for the exact same session it can differ by over a litre.

What Dehydration Actually Does to Your Performance

Losing fluid equal to just 2% of your body weight is enough to cause a noticeable dip in how you perform. The Better Health Channel from the Victoria State Government notes that for someone who’s 70kg, that’s a loss of 1.4kg—barely two pints. That’s all it takes. When your body water drops below normal, you can’t regulate your heat as well, you get tired quicker, your decision-making suffers, and your sports performance falls off a cliff.

The early warning signs, as listed by Medical News Today and StatPearls, include feeling thirsty, your urine getting darker, not needing to pee as often, headaches, feeling sluggish, feeling dizzy, and even constipation. One sign that’s easy to miss is if you stop sweating during a hard effort when you really should be sweating. Treat that as a stop-what-you’re-doing signal, not a push-through one. It’s a clear red flag that your body’s cooling system is packing up.

The Other Failure Mode: Drinking Too Much

We get told a lot about dehydration, but drinking too much water during exercise is its own serious problem. It’s called exercise-associated hyponatraemia, or EAH. PM&R KnowledgeNow defines it as blood sodium dropping below 135 mmol/L during activity or within 24 hours after. The way it happens is pretty straightforward: you keep drinking low-sodium fluid for ages, and because of a hormone called arginine vasopressin your body can’t get rid of the excess water. Whenever you’re taking in fluid faster than your body can pee it out, your blood sodium gets diluted.

The confusing part, as the Gatorade Sports Science Institute points out, is that the symptoms—feeling tired, bloated, sick—are really similar to dehydration. So people think they need to drink more, which just makes things worse. The big difference is that with EAH you actually put on weight during a session instead of losing it. That’s exactly why weighing before and after is such a smart move. The group often most at risk are the slower participants in long events, like marathons or charity walks, who drink at every single drinks station "just to be safe."

Salty Sweaters and When Electrolytes Matter

For sessions under about an hour, water is fine for most people. But once you get beyond that 60–90 minute mark, especially in the heat or if you’re a heavy or salty sweater, replacing sodium becomes important. The Gatorade Sports Science Institute explains this helps your body hold onto the fluid you’re drinking and also cuts the risk of EAH. A practical sign you’re a salty sweater is seeing white tide marks on a dark training top, or getting really stinging eyes from your sweat. If that sounds like you, an electrolyte tablet or a sports drink is a good idea for longer efforts.

Your Simple Hydration Plan

You don’t need a complicated spreadsheet. Here’s a straightforward plan based on the research.

• 2 hours before: Drink about 500ml.
• During: Sip 200–300ml every 15 minutes (or 0.4–0.8 litres per hour), rather than chugging a whole bottle at once.
• After: Drink to thirst, and have a salty meal. If you weighed yourself, aim to replace roughly 1.25–1.5 litres for every kilogram of weight lost.
• Everyday baseline: Stick to 6–8 glasses and aim for pale straw urine.

Frequently asked questions

Does coffee or tea dehydrate you?

No. The NHS counts tea and coffee as part of your daily fluid intake. Caffeine is a mild diuretic, sure, but the water in the cup more than makes up for it, so your brew still goes towards your 6-8 glasses.

How much water should I drink after a workout?

The most accurate way is to weigh yourself before and after. Aim to drink 1.25 to 1.5 litres for every kilogram of body weight you lost. If you didn’t manage to weigh in, just drink to your thirst and have a salty snack or meal to help your body hang onto that fluid.

Is it possible to drink too much water while exercising?

Yes. Drinking way more than you’re losing in sweat can bring on exercise-associated hyponatraemia, which is a dangerous drop in your blood sodium. Symptoms like feeling bloated and sick can look a lot like dehydration, which is why getting on the scales is a really important safety check.

What's the easiest way to check if I'm dehydrated?

The colour of your urine is your best daily check. You’re aiming for a pale straw or light yellow colour. Dark yellow or amber is a clear signal you need to drink more.

Do I need sports drinks for every workout?

For workouts that last under an hour, water is enough for most people. For longer sessions, particularly when it’s hot, or if you’re someone who sweats a lot, a drink with electrolytes—especially sodium—can help you stay hydrated and keep your performance up.

How do I calculate my personal sweat rate?

Weigh yourself in minimal clothing before you exercise and then again straight after, making sure you towel off first. The weight you lost in kilograms is roughly the litres of sweat. Then you add back any fluid you drank during the session to get your total sweat loss for that workout.

The bottom line

Getting your hydration right for training boils down to a few actionable steps. Start by knowing your baseline with the pale straw urine test. Before you train, drink 500ml two hours ahead. During your session, follow the 200-300ml per 15-minute rule, sipping steadily. The single most valuable thing you can do, though, is to weigh yourself before and after a couple of your regular workouts. That simple act gives you your personal sweat rate—a number more useful than any generic guideline. It removes the guesswork, helps you avoid the performance drag of dehydration, and guards against the risks of overdrinking. Your next session is the perfect time to start.