Sweating all day working outdoors: what should I drink?

If you sweat all day working outdoors, water is the main thing to replace, and Thai studies show how easily outdoor workers fall behind. In one study of sugarcane cutters, the share with signs of dehydration in their urine rose from 16.7% before a shift to 53.3% after it, even though they drank an average of 3.8 litres during the shift. The US workplace health agency NIOSH advises, for moderate work in the heat lasting under 2 hours, 1 cup of water every 15 to 20 minutes and generally no more than 6 cups an hour, and a sports drink with balanced electrolytes if sweating goes on for several hours. Keep meal breaks, plan the heaviest work for cooler hours, and learn the signs that mean you should stop.

This article is about water, salt and the heat. For protecting your skin from the sun at work, see Working in the sun all day: can I protect skin from inside? For tiredness from long, heavy workdays in general, see Tired all day from work and mentally drained: what can I do? For the sodium in Thai food, see Love salty food and can't cut back? What can you do?

How much water do I lose when I sweat outdoors all day?

Sweat is mostly water, with salt

Sweating is how the body cools itself in the heat. Sweat is mostly water, and it also carries salt: the UK's NHS notes that an isotonic sports drink or oral rehydration powder mixed with water helps replace salt lost through sweating.

US MedlinePlus names heavy sweating as one reason the body's fluid and electrolyte balance can be upset, and explains that the water you take in should equal the water you lose.

Everyone sweats differently

The American College of Sports Medicine notes that sweating rates and the amount of salt in sweat vary considerably between people. Two workers doing the same job in the same field can lose very different amounts. That is one reason fixed amounts are only a starting point.

A simple check: weigh yourself

The same position stand explains that your own sweat rate can be estimated by weighing yourself before and after activity, and it aims to keep water loss from going beyond 2% of body weight. If you have scales at home, weighing yourself before and after a long shift shows how much water you did not replace.

What do Thai studies show about outdoor workers and the heat?

Findings from Thai workplaces

What the studies have in common

These studies looked at particular jobs in particular provinces, most at one point in time, and symptoms were self-reported. But the pattern is consistent: long hours in the heat, heavy work and too little water go together with symptoms. The sugarcane study also shows that even 3.8 litres a shift was not enough for many cutters to finish the day without signs of dehydration. Phanprasit and colleagues also report that maximum temperatures in Thailand rose from 38 to 41°C to 42 to 44°C between 2001 and 2016, so these conditions are not getting easier.

How much should I drink while working outdoors, and what?

NIOSH's guide for work in the heat

Drinking at set times means you are not relying on thirst alone, and the field studies above show how easy it is to fall behind.

Check your urine colour

The UK's NHS suggests drinking more in hot conditions or during long physical activity than the usual guide of 6 to 8 glasses a day, and aiming for urine that is a clear pale yellow. Dark urine at the end of a shift is a sign you drank less than you lost.

Iced coffee, sweet tea and energy drinks

Iced coffee, cha yen and energy drinks are part of many working days in Thailand. NIOSH advises avoiding drinks with high caffeine or sugar while you work in the heat, and the US CDC suggests limiting drinks high in sugar or sodium, caffeine and alcohol on hot days. They can be part of your day, but they are not a replacement for water during the shift. Keep beer and other alcohol for well after work.

Practical ways to keep drinking

• Keep a large bottle of water where you work and refill it at every break.
• Drink a cup at set times, for example every time you finish a row, a load or a delivery.
• If water at work is warm or hard to reach, ask your employer about it: NIOSH advises employers to provide enough cool drinking water near the work area.

What should I know about the salt lost in sweat?

How much sodium Thai adults take in

A nationwide survey of Thai adults that measured sodium in 24-hour urine, by Chailimpamontree and colleagues (2021), found an average intake of 3,636 mg of sodium a day, which the authors describe as nearly twice the recommended level. The Thai Reference Daily Intake (Thai RDI) for sodium is 2,000 mg a day. This is an average for adults in general; the survey did not look specifically at people who sweat heavily at outdoor work.

When an electrolyte drink makes sense

NIOSH's advice is specific: when sweating lasts for several hours, drink sports drinks containing balanced electrolytes.

The American College of Sports Medicine notes that the amount of salt in sweat varies considerably between people, so what suits one worker may not suit another.

Keep your meal breaks

On a hot day it is tempting to skip lunch and keep working, or to eat only a sweet drink. Regular meals give you food and fluid, and the break itself is time out of the heat.

How can I plan the workday around the heat?

Heavy work in cooler hours

In the sugarcane field study, heat measured as WBGT (a measure that combines temperature, humidity, sun and wind) averaged 30.6°C between 7:30 and 17:30, rose until noon, stayed above 30°C through the afternoon and began to fall after 15:30. Where you have a choice, do the heaviest tasks early in the morning or later in the afternoon, and take breaks in the shade during the hottest hours.

Get used to the heat gradually

NIOSH advises building up time in the heat over the first days on a new job. New workers should spend no more than 20% of the usual time in the heat on day 1, then increase by no more than 20% each day. Workers who have worked in the heat before should spend no more than 50% on day 1, 60% on day 2, 80% on day 3 and 100% on day 4. For more on this, see Working in the sun all day: can I protect skin from inside?

Clothing and working in pairs

In the study of 200 sugarcane farmers, those wearing two layers of shirts were more likely to report symptoms from the heat. Light, breathable layers that still cover the skin are a reasonable balance between sun protection and heat. NIOSH also recommends a buddy system, where workers keep an eye on each other for warning signs.

Rest after work

Heat at work can follow you home: a review of 11 studies of heat-exposed workers found that night-time temperatures above 25°C and high heat at work were linked with poorer, more delayed sleep. For ways to cope with hot nights, see Hot nights and can't sleep: what can I do?

What are the danger signs, and when should I get help?

Signs to stop and cool down

The NHS lists these signs that the heat is getting to you: tiredness, dizziness, a headache, feeling or being sick, heavy sweating, pale and clammy skin, cramps in the arms, legs or stomach, a high temperature, being very thirsty and feeling irritable. If you or a co-worker notice them, the NHS advises:

1. move to a cool place
2. take off unnecessary clothing
3. drink plenty of water (a sports drink is also fine)
4. cool the skin with cool water and fan it

People should start to feel better within 30 minutes.

Call 1669 straight away if

• the person is confused or not making sense, or has a fit
• they pass out
• their skin is hot and they are not sweating
• they have a very high temperature, a fast heartbeat, or fast breathing or shortness of breath
• they are still unwell after 30 minutes of resting somewhere cool

While you wait, move them somewhere cool and keep cooling them with water.

See a doctor if

• you often feel dizzy, sick or faint at work even when you drink and take breaks
• you take regular medicines and are not sure whether they affect how you cope with heat (do not stop them on your own)
• you see a doctor regularly about your health and work in the heat
• you are pregnant or breastfeeding, or take regular medicines, and want to change what you drink at work, such as having electrolyte drinks every day: ask a doctor or pharmacist first