Hydration for Runners: How Much, When and What (UK 2026 Beginner Guide)

Walk into any running shop in the UK and you will be sold a hydration vest, a bladder, three flavours of electrolyte tab and the strong suggestion that you must drink at every kilometre or you will fall over. Most of this is nonsense for beginners. The science of running hydration is far simpler, far less expensive, and far less dramatic than the marketing suggests. For most of the runs a beginner does in normal British weather, water before the run and water after the run is genuinely all you need.

The biggest hydration mistake beginners make is not under-drinking. It is over-drinking. Forcing down a litre of water in the 30 minutes before a 5K leaves you sloshing, breathless and needing the toilet at kilometre two. Sipping a sports drink every five minutes on a 40-minute run does nothing useful for your performance. And the famous 8-glasses-a-day rule, which has stalked British wellness culture for 80 years, has no scientific basis whatsoever. Your body is rather good at telling you when to drink. It uses a feature called thirst.

What you do need to know is when hydration genuinely matters, which is on long runs, hot runs, and the 24 hours before any run. You also need to know when electrolytes earn their keep, which is rarer than the brands would like you to believe. And you need a sensible way to spot real dehydration when running, separate from the normal tired-legs feeling of a hard session. This guide covers all of that, with no upsells.

Sources: NHS Eatwell Guide hydration advice; American College of Sports Medicine position stand on exercise and fluid replacement; Edge member data, May 2026.

How much to drink before, during and after a run

There are three windows that matter for running hydration. The 24 hours before the run, the run itself, and the two hours after. Get the first one right and the second one almost takes care of itself. Get the third one right and you protect tomorrow's training too.

1. The 24 hours before

This is where most beginners win or lose their hydration game, and they do not even realise it. Your goal in the day before a run is steady, low-key fluid intake spread across the whole day. For an adult, that means around two to three litres of total fluid, including tea, coffee, water and the water in food. Yes, tea counts. The old myth that caffeine dehydrates you is wrong for the doses most people drink. Two or three cups of tea contribute to your daily fluids, they do not subtract from them.

Steady is the keyword. Sipping a glass of water every hour or two during the day puts you at the start line in good shape. Downing a litre 20 minutes before you head out the door does not. Your kidneys cannot process that much that quickly, so most of it sits in your stomach feeling unpleasant, or makes a quick exit before you have even warmed up. If you wake up and your urine is pale straw colour, you are fine. If it is dark yellow, drink a glass of water and wait 30 minutes before you run.

2. During the run

For most runs a beginner does in normal UK weather, the answer here is genuinely nothing. If you have hydrated reasonably during the day, a 30, 40 or 50 minute run does not require mid-run drinking. You will not improve your performance. You will not protect your health. You will mostly just have to carry a bottle for no reason.

The threshold beyond which mid-run hydration starts to matter is around 60 minutes, and even that is conditional on conditions. A 65-minute run in 12 degree March weather still needs no water. A 50-minute run in 28 degree July heat absolutely does. If you are running over 60 minutes, or temperatures are above about 22 degrees, the guideline is 150 to 250 ml of water every 20 minutes, sipped rather than gulped. The calculator above gives you a number tailored to your run.

3. The two hours after

Most beginners forget the after window completely, which is a shame because it is the cheapest performance gain in running. Within the first two hours after you finish, your muscles are most receptive to refuelling and rehydrating. A glass of water and a snack with some salt in it, like a slice of toast with peanut butter or a normal meal, replaces fluid and electrolytes much better than gulping plain water alone.

A simple test is to weigh yourself before a long or hot run and again after. Any weight loss is fluid loss. Replace it at roughly 500 ml of fluid per half kilogram lost over the next few hours, alongside your normal eating. For shorter runs, this is overkill. A glass of water and a meal is plenty.

When electrolytes actually matter for runners

Electrolytes are minerals, mainly sodium, potassium, magnesium and chloride, that your body needs to keep nerves firing and muscles contracting. You lose them in sweat. The marketing for electrolyte products has expanded dramatically in the last few years, and most of it is selling you something you genuinely do not need on a 30-minute run. There are three situations where electrolytes earn their place.

1. Runs over 75 minutes

At some point past about 75 minutes of continuous running, the volume of sweat you have lost starts to mean a meaningful drop in your sodium levels. Drinking pure water at that point can actually dilute your sodium further, which over a long enough period can cause symptoms ranging from mild nausea to, in rare extreme cases, hyponatraemia. For runs over 75 minutes, an electrolyte tab in your bottle, or a small amount of sports drink, replaces what you have sweated out and keeps everything balanced.

2. Runs in 22 degrees or higher

Heat dramatically increases sweat rate. A 45-minute run on a 26 degree afternoon can produce as much sweat loss as a 75-minute run on a cool day. The same logic applies. If you are sweating a lot, you are losing not just water but salts, and pure water alone is not the best replacement. In UK summer heat, electrolytes start to matter at shorter durations than they would in winter.

3. Heavy sweaters

Some people sweat much more, and much saltier sweat, than others. If you regularly finish runs with white salt crusts on your face, sweat that stings your eyes badly, or a salty taste on your skin, you are what coaches call a heavy salty sweater. You will benefit from electrolytes sooner than the average runner, even on runs of 45 to 60 minutes in mild weather. This is genetic and not a sign of fitness or unfitness. Some elite runners are heavy sweaters. Some beginners are not. Learn your own pattern and dose accordingly.

Most beginners think they are dehydrated when they are tired. Hydrate the day before, and most runs need no mid-run drinking at all.

What to drink: water vs sports drink vs electrolyte tabs

Walk into a supermarket and you will see a wall of drinks aimed at runners, from neon sports drinks in 500 ml bottles to single-serve electrolyte tabs to bottled "endurance fuel" with prices that suggest it contains gold. Here is the honest hierarchy for a beginner.

1. Plain water

For any run under 60 minutes in normal UK weather, plain water is genuinely the right choice. Tap water is fine. Bottled water is fine. There is no meaningful performance difference between them for any run a beginner is doing. Save your money. Drink a glass before you head out if you feel like it, drink another when you get back, and that is your hydration strategy sorted.

2. Electrolyte tabs

For runs over 75 minutes, hot runs, or if you are a heavy sweater, a single electrolyte tab in 500 ml of water is the simplest, cheapest, most flexible option. Brands like SiS, High5, Precision and the cheaper supermarket versions all do the basic job. Look at the sodium content per tab, which should be roughly 200 to 500 mg. Higher numbers are aimed at marathon runners and ultra athletes, not beginner 10K trainees.

3. Sports drinks

Pre-mixed sports drinks combine water, electrolytes and carbohydrates, which makes them useful on runs over 90 minutes when you are also looking for fuel. For shorter runs, they are mostly sugar water with marketing. The sugar load can also upset some stomachs mid-run, so test them on a training session before any race. For most beginner runs of under an hour, a sports drink is overkill.

The 8-glasses-a-day myth, finally explained

You have heard it a thousand times. Drink eight glasses of water a day for good health. It is one of the most repeated pieces of British wellness advice and it is, for almost everyone, complete nonsense. The origin is a 1945 US Food and Nutrition Board recommendation that adults need about 2.5 litres of water a day, with the crucial extra sentence that most of this would come from food. That second sentence was repeatedly cut, and a quote about total fluid intake became a stern instruction to drink eight glasses of water on top of everything else.

The actual evidence on hydration is much calmer. Thirst is a reliable signal in healthy adults. Your kidneys are excellent at managing your fluid balance over the day. Most adults get about 20 to 30 percent of their daily fluid from food alone, mostly from fruit, vegetables, soup and porridge. Add in a few cups of tea or coffee, a glass of water with meals, and a drink during exercise, and you are easily at the 2 to 3 litre total fluid intake that the science supports.

The practical takeaway for runners is to stop measuring your hydration in litres of water. Measure it instead by the colour of your urine across the day. Pale straw colour is the target. Dark yellow means drink a glass. Completely clear means you are probably over-drinking, which is rarer than under-drinking but absolutely possible, especially among nervous runners trying to hyper-hydrate before a parkrun.

Signs of dehydration when running

Real dehydration on a run feels distinct from the normal tired-legs sensation of a hard session. The mild signs are easy to spot once you know them. The severe signs are rarer and they matter enormously, so they need their own paragraph at the end.

• Dark urine in the hours before your run. Pale straw is the target.
• Persistent headache that started before or during the run.
• Dry mouth beyond the normal mouth-breathing dryness of running.
• Dizziness when you slow down or stop, especially on standing up.
• Cramping in your calves, hamstrings or feet, particularly in heat.

If you spot any of these mid-run on a long or hot session, walk for a few minutes, sip water with an electrolyte tab in it, and reassess. The vast majority of these symptoms clear within 10 to 20 minutes of slowing down and drinking sensibly.

Carrying water on long runs

Once your long runs creep past 60 minutes, particularly in summer, you will need to think about how to actually carry your water. There is no single right answer. The right one for you depends on where you run, how far, and what you find comfortable on your body.

1. Handheld bottles

A 250 to 500 ml handheld bottle with a strap that wraps over your hand is the cheapest, simplest option for runs of 60 to 90 minutes. Brands like Nathan and Salomon make them, and supermarket versions exist too. The downside is that one hand is always full, which some runners hate. The upside is you can ditch it easily, refill it at a fountain, and there is no kit to wash and dry.

2. Hydration vests

For runs over 90 minutes, particularly trail or rural routes with no shops, a hydration vest with two soft front flasks is the standard solution. They sit close to the chest, do not bounce much once fitted properly, and give you 1 to 1.5 litres of capacity. Expect to spend £60 to £120 on something decent. Try it on with the flasks full before you buy. Many runners size up by one.

3. Route with water fountains

The hidden third option in the UK is route planning. Many parks, particularly in London and Manchester, now have refillable water fountains as standard. The Refill app shows fountains and friendly shops on a map. Planning a long route that loops past a fountain at the 45 minute mark means you can run with a single 500 ml bottle, top up halfway, and finish without needing kit at all. For city runners this is often the most practical answer.

How Edge helps if you have hydration questions

Edge does not bake hydration cues into every session, and it does not auto-adjust your plan to the forecast. What it does do is give you Edge AI, which is a direct line to the coaches. Type a question in plain English ("It is going to be 26 on Saturday, what should I drink before and during?") and Edge AI gets you a coach-grade answer in under 30 seconds. If the answer changes the week, you can use Flexi Swap to move sessions around your week with a couple of taps.

Strength, mobility and the running plan itself are all built in. The hydration knowledge sits behind Edge AI, the way it would with a real coach. Edge has a free 7-day trial, then costs £19.99 per month or £119.99 per year. Over 17,000 UK members already train with Edge. Try Edge free.

Hydration for runners: frequently asked questions