Hydration for 10K to Half-Marathon

Hydration for 10K to Half-Marathon

We all know good hydration helps in improved performance during the race. As 10K usually lasts closer to 60 min, the impact of dehydration may not be significant. However, in a half marathon, the time is more than 60 min and hence proper focus must be put on hydration.

There are various factors that decide the hydration strategies such as Body weight, Sweat rate, Training or race day temperature and humidity and Training history.

This article provides broad guidelines for hydration and can be tailored for individual needs after assessment of various parameters.

Factors that influence hydration

Three States of Hydration

Our body can be in three different states of hydration based on how we hydrate ourself before, during and after the race. Here is a quick summary of these states, how to identify which state we are in, and how that impacts performance.

States of hydration

During most races and training days, light de-hydration is expected and it does not hamper performance. But we need to be careful of extreme dehydration or over-hydration.

Hydrating for a Mid Distance Race

There are 2 schools of thought on Hydration.

  1. Drink when thirsty
  2. Drink before feeling thirsty to prevent dehydration

Both these thoughts have their merits. We will tread the middle path.

So here are our pointers, keeping in mind that good hydration practices during the training are very much recommended to prepare for race days.

Hydration guidelines

Hydration during 10K race

Hydration during 10k

Sweat Rate

Before we delve into hydration for the half-marathon, we need to understand sweat rate. If we lose more water due to our sweat (and pee) than we are able to replace the water in our body (and cells), then we risk dehydration. Hence estimating our water loss due to sweat and pee becomes crucial at this point.

Calculation of Sweat Rate (water loss per hour)

Here is how you can estimate water loss per hour due to your sweat and pee (during the training or race)

1 kilo of water = 1 litre of water in volume.

Take measurements:
  • Initial Weight: Measure yourself in minimum clothing before training or race. Ex: 65 kilos.
  • Food and water intake: While training measure all the food and water you have consumed. Ex: Water consumed 0.5 litre, which is approx. 0.5 kilo; Ex: 2 Bananas, 5-6 inches in length, consumed would be approximately 150-200 grams.
  • Time in training: Measure the time taken for your training. Ex: 90 min.
  • Final Weight: Measure yourself in minimum clothing after workout or race. Ex: 64 kilos
Calculate the water loss:

Water loss (due to sweat or pee) = Weight before workout + any water or food consumed – weight after workout.

Water loss rate = Water loss / Total time taken for workout

Let’s apply the calculation in the above example

Water loss = 65 (Bodyweight) + 0.5 (0.5 litre of water) + 0.2 (bananas) – 64 = 1.7 kilos

Water loss rate = 1.7 / 1.5 = 1.13 kilo/hour (or) approximately 1.13 litre per hour (or) 0.28 litre per 15 min. In short, around 300 ml per 15 min.

Based on the above calculation, one has to consume 300ml of hydration every 15 min.

It might be difficult to increase 300 ml of water suddenly and so quickly. So one has to phase out the water consumption in a gradual manner – one gulp at a time every 15-20 min.

Hydration during Half-Marathon

Hydration during half-marathon

What to drink?

There are 3 concentrations of water that can impact the level of hydration in your body.

Concentrations of water


From the above table, you might ask, why not drink plain water to ensure maximum hydration. In the 3 states of hydration, we talked about over-hydration that can lead to salt imbalances in our body causing hyponatremia. So our water must have enough salt and other minerals to balance the salt inside our cells in the body.

We can play with the concentration of water by adding ‘salts’ to it. Adding a pinch of salt (NaCl or Sodium Chloride) is good to make the water hypotonic and improve the absorption rate. However, during endurance runs, we need more than common salts. We need a few more minerals such as Potassium, Calcium, and Magnesium, to improve the functioning of muscles and nerve cells. This is where the role of proper electrolyte comes in. A simple ORS (Oral Rehydration Solution) has most of these minerals in the right amount to create an awesome hypotonic and maybe even an isotonic drink. Please read the instructions carefully while preparing the ORS as you may not want to increase your concentration.

Here is a table that can help you choose the appropriate hydration.

Hydration Indices

Closing Notes

  • There are various metrics to measure how hydrated you are. So be self-aware by checking your hydration using the pee colour as guidelines as it is far easier.
  • If you sweat a lot, connect with a nutritionist to plan your hydration strategy.
  • Train in various heat, humidity, and dehydrated states before the race events.
  • While running the brain cannot do so many calculations as it is stressed and tired. So, have a simple strategy to hydrate during the run. + Don’t overcomplicate it. For example, instead of hydrating at a certain time, hydrate using distance as a measure, because most aid stations are between 2-3 kilometers.


Sujoyjeet is a certified nutritionist and a personal trainer. To provide actionable insights to clients, he understands his clients lifestyle before providing a habit-based nutrition plan. The habit based nutrition plan teaches his clients how , what & when to eat and why to eat certain specific foods to meet their health, performance and body composition goals.

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