Living somewhere that is hot all year changes how much fluid you lose, but the advice around hydration is often confusing or aimed at selling something. The basics are simpler than they seem.

Everyday hydration

For ordinary days, including commuting and walking around the city, thirst is a reasonably good guide. Drink when you are thirsty, have water with meals, and keep a bottle with you. Pale yellow urine is a sign you are doing fine. Very dark urine, headaches in the afternoon or feeling unusually tired can be signs you are behind.

Bangkok tap water is treated at source but the pipes in older buildings are not always reliable, so most people use filtered or bottled water. Refill stations in condos and on streets are cheap and reduce plastic.

When sweat losses add up

Sweat is mostly water but also contains sodium and smaller amounts of potassium. In a temperate climate, a one-hour workout rarely creates a problem. Here, a long run, a Muay Thai session or a day of hiking can produce two or three litres of sweat. Replacing that only with plain water can dilute the sodium in your blood, which in rare cases becomes dangerous and more commonly just leaves you feeling flat and crampy.

For sessions longer than about an hour in the heat, or if you notice white salt marks on your clothes, add some electrolytes. That can be an oral rehydration salt sachet from any pharmacy, a sports drink, or simply salty food with your post-workout water. Thai food is helpfully generous with salt; a bowl of noodle soup after training does real work.

Do not overdo it

Drinking large amounts of water without being thirsty does not make you healthier. Aim to replace losses over the hours after exercise rather than forcing litres in one go. A rough guide is to drink about one and a half times the weight you lose during a session, spread out over the following few hours.

Alcohol, caffeine and the heat

Coffee in normal amounts counts toward your fluid intake. Alcohol is different: it increases fluid loss and impairs your judgement about heat. A long afternoon of beers by the pool followed by a big night out is a classic way to feel terrible the next day. Alternate with water and eat properly.

Who should be more careful

People taking blood pressure medication or diuretics, those with kidney or heart conditions, older adults and anyone pregnant should talk to their doctor about fluid and salt intake in a hot climate, since general advice may not apply.