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Hydration Plan for Your Triathlon Race

7 min read 8 sections Nutrition

Dehydration is invisible until it is too late. You will not feel parched on the bike at mile fifteen — you will feel it as a dead run at mile twenty-two. This guide shows you how to calculate your sweat rate, plan your hydration intake by distance, and arrive at the finish line still coherent.

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Why hydration matters more than you think

A 2% loss of body water (dehydration) reduces aerobic performance by up to 20%. A 3–4% loss causes cognitive impairment: you make bad pacing decisions, you miss nutrition cues, and you slow significantly on the run. Most age-group triathletes arrive at the run 3–5% dehydrated because they drank less than their sweat loss on the bike.

The goal is not to drink as much as possible. The goal is to drink enough to replace 80–90% of your sweat loss without over-hydrating, which can cause hyponatraemia (dangerously low blood sodium).

Calculate your sweat rate

Your sweat rate depends on your body size, fitness level, genetics, and environmental conditions. The only accurate way to measure it is in training. On the day you test, wear similar clothing to what you will race in, control the intensity (race pace), and account for weather.

The test: weigh yourself completely dry before a one-hour workout. Consume a measured amount of fluid during the hour. Weigh yourself again immediately after (dry towel). The weight difference plus the fluid consumed is your sweat loss for that hour.

Test sweat rate in conditions similar to your race (temperature, terrain, intensity).

Account for the fluid you drank: (pre-weight – post-weight) + fluid consumed = sweat loss.

Test multiple times and take an average — sweat rate varies day to day.

A 70 kg athlete losing 1.5 kg in an hour is sweating 1500 ml/hour; a 60 kg athlete losing 1 kg/hour is sweating 1000 ml/hour.

Hydration targets by distance

Once you know your sweat rate, your hydration target is simple: drink 80–90% of your sweat loss per hour. On the bike, this is usually achievable because you can carry bottles and access aid stations. On the run, it is harder because you cannot carry as much fluid and your stomach is more sensitive to volume.

Sprint (up to 90 min): 400–600 ml per hour; aim to drink at aid stations.

Olympic (120–150 min): 500–800 ml per hour on the bike, 300–500 ml per hour on the run.

70.3 (4–5 hours): 500–1000 ml per hour on the bike (depends on temperature and sweat rate); 300–600 ml per hour on the run.

Full Ironman (8–17 hours): 400–1000 ml per hour on the bike (adjust for temperature); 300–600 ml per hour on the run.

Fluid delivery: bottles, hydration packs, or aid stations?

On the bike, you have options: a frame-mounted bottle, a hydration pack, or reliance on aid stations. On the run, most athletes use aid stations and carry a handheld bottle if needed for hot conditions.

The key is knowing your plan before race day. If you plan to carry two bottles on the bike and swap at aid stations, practise that. If you use a hydration pack, make sure it does not rub your shoulders in a race suit.

Bike: one or two frame bottles + aid station refills, or hydration pack.

Run: aid station reliance, or a handheld bottle for personal preference.

Test your fluid delivery system in long training sessions.

Confirm your fluid brand is available at race-day aid stations.

Electrolytes: sodium is not optional

Plain water is not enough for efforts longer than ninety minutes. You lose sodium in sweat, and replacing it with water alone dilutes your blood sodium further — a dangerous condition called hyponatraemia.

Every drink should contain electrolytes, especially sodium. Most sports drinks contain 20–30 mmol of sodium per litre. Aim for 500–700 mg of sodium per litre of fluid, depending on your sweat loss and salt sensitivity.

For efforts over 90 minutes, every fluid should contain sodium.

Sports drinks typically contain sufficient sodium; plain water does not.

Some athletes prefer electrolyte capsules or salt tablets with water.

Test your electrolyte product in training — some cause GI upset if concentration is too high.

Hydration during the run: the challenge

Your stomach is bounce and sensitive when running. You cannot carry as much fluid as on the bike. And the constant impact of running makes digestion harder. Many athletes accidentally under-hydrate on the run because drinking feels difficult.

The solution: drink small, frequent amounts (100–150 ml) every 10–15 minutes at aid stations rather than trying to slam a large volume at once.

Take a cup at every aid station — even if you do not feel thirsty.

Drink 100–150 ml every 10–15 minutes, not 500 ml once an hour.

Walk aid stations if necessary to drink without sloshing.

Use a handheld bottle if you prefer consistent sipping over aid-station reliance.

Urine colour: your hydration dashboard

During race day, you cannot measure your exact hydration status. But you have a simple visual check: urine colour. Pale yellow indicates adequate hydration. Dark yellow means you are behind. Clear means you are over-hydrating.

Check this at every stop. If you are dark, increase your intake slightly. If you are clear and experiencing bloating, dial back the volume.

Pale yellow = hydrated, on track.

Dark yellow = behind; increase fluid intake.

Clear = over-hydrating; reduce volume or increase electrolyte concentration.

Check at every aid station where there is a toilet.

What to do if you get dehydrated

You have been drinking, but the heat or your sweat rate got ahead of your intake. You feel heavy-legged, your run pace has dropped, and everything hurts. You are dehydrated, and the run is still three miles away.

Do not panic. Slowing down slightly and increasing your fluid intake for the next 10–15 minutes can recover some of your hydration status. It is not a complete fix, but it reduces the depth of the hole you are in.

If dehydrated: walk the next aid station, take 200–300 ml of fluid with electrolytes, slow your pace for 5 minutes.

If severely dehydrated: focus on finishing, not racing. Walk, drink at every station, and congratulate yourself for not DNF-ing.

● Race Preprr

In Race Preprr, mark every aid station location on your run so you know exactly when you will have access to water and can plan your hydration timing accordingly.

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● Try it free

Map your hydration strategy in Race Preprr
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Identify every aid station, plan your fluid intake by distance, and carry your hydration targets with you on race day.

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