Gym water in the tropics: how much to drink during a workout

In short: an hour of training in a hot gym costs you 0.5 to 1.5 L of fluid along with salts. The plan is simple: 300 to 500 ml an hour before the session, a couple of mouthfuls every 15 to 20 minutes during it, and the rest afterwards. Mineral water of moderate mineralisation is handy because it brings back both the water and the minerals.

How much fluid do you lose in an hour of training?

An hour of training in a hot gym costs you 0.5 to 1.5 L of fluid. It is easy to check: weigh yourself before and after, and every kilogram lost is roughly a litre of water. In a gym without air conditioning in Phuket you will sweat more than in your usual gym back home. Sodium, potassium and magnesium leave along with the water, so water alone does not always settle the question: cramp in the calves often comes with dehydration and a shortage of salts.

• Weigh yourself before and after training: every kilogram "lost" is a litre of fluid
• In a gym without air conditioning in Phuket you sweat more than in a gym back home
• Sweat takes away sodium, potassium and magnesium, not just water
• Cramp in the calves often comes with dehydration

A drinking plan

A simple plan works: 300 to 500 ml an hour before training, 150 to 250 ml every 15 to 20 minutes during it, and the rest steadily over the hour or two afterwards. Downing it in one go is not the way, since the water is absorbed less well and gets in the way of the session. During exercise, cool water goes down more easily than ice-cold. If you weighed yourself before and after, the guide is the same: however many kilograms went, put back that many litres by the end of the day.

• 300 to 500 ml an hour before training
• 150 to 250 ml every 15 to 20 minutes during it
• Afterwards, steadily over an hour or two rather than in one go
• During exercise, cool water is easier to drink than ice-cold

When water alone is not enough

There are cases where plain water does not cover it. A session longer than 90 minutes, heavy CrossFit or a run in the heat: here people take mineral water or an isotonic drink to put the salts back. Plan morning runs with a margin, since there may be no water on your route. If you drink plenty and still feel dry and crave something salty, it is usually about salts rather than volume. These are general guidelines, so work out your own routine with a coach and a doctor.

• If the session runs longer than 90 minutes or it is heavy CrossFit, take mineral water or an isotonic drink
• Morning runs in the heat: work out the volume in advance, as there may be no water on the route
• If you drink plenty and still feel dry, it is probably salts you are short of, not water
• These are general guidelines. Work out your own routine with a coach and a doctor

What to take with you

For the gym, take something unbreakable: still water in 0.5 L PET, Icelandic Glacial or 6ty Degrees, or your own flask. It fits the holder and you can see at a glance how much you have drunk. If you go every day, an 18.9 L bottle at home or at the gym works out cheaper than buying bottles one at a time: you fill the flask from it. After a hard session, mineral water with magnesium and calcium is handy: Narzan's label gives 50 to 180 mg/L of magnesium and 200 to 600 mg/L of calcium. It comes in 0.45 L glass, so it is one to drink back at home. A glass or two is enough, then carry on with ordinary water.

• 0.5 L PET or your own flask: unbreakable, fits the holder, and you can see at a glance how much you have drunk
• An 18.9 L bottle at home or at the gym works out cheaper than buying bottles one at a time
• Mineral water with magnesium and calcium after a hard session

Sources

• GOST R 54316-2020: composition of Narzan water (table A.1)
• EFSA: water intake reference values (2010)