heat stress

Hydration

Drinking enough fluids is one of the most important things you can 

do to prevent heat illness. Water is generally sufficient for hydration.

Hydrate Before Work

• Being hydrated when you start work makes it easier to stay hydrated through

the day.

• If you are dehydrated when you start work, you may not be able to drink

enough to catch up with your body’s need for water.

Hydrate During Work

• Drink before feeling thirsty. By the time you feel thirsty, you are already

behind in fluid replacement. Dehydration is a primary contributor to

heat exhaustion.

• Your work performance may suffer when you

are dehydrated, even if you don’t notice.

• When working in the heat, drink 1 cup

(8 ounces) of water every 15–20 minutes.

• This translates to 3⁄4–1 quart (24–32 ounces)

per hour.

• Drinking at shorter intervals is more effective

than drinking large amounts infrequently.

• Do not drink more than 48 oz (11⁄2 quarts) per hour! Drinking too much

water or other fluids (sports drinks, energy drinks, etc.) can cause a medical

emergency because the concentration of salt in the blood becomes too low.

How much water is that?

1 

quart = 1/4 gallon

(32 oz) =

approx

1 

L

Hydrate After Work

• Most people need several hours to drink enough fluids to replace what they

have lost through sweat. The sooner you get started, the less strain you place

on your body from dehydration.

• Hydrating after work is even more important if you work in the heat on a

regular basis. Chronic dehydration increases the risk for a number of medical

conditions, such as kidney stones.

Urine

Color

Test WELL HYDRATED HYDRATED DEHYDRATED Drink water! SEVERELY DEHYDRATED Drink water immediately!

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heat stress Hydration

What to Drink

Water

Water will almost

always maintain

hydration during

work in the heat,

as long as you eat

regular meals to

replace salt lost

in sweat.

What to Avoid

Energy Drinks

• Some energy drinks contain much

more caffeine than standard servings 

of coffee, tea, or soft drinks.

• Drinking several energy drinks per

day can raise your caffeine levels

enough to affect your heart. High

caffeine levels can be risky when

added to the strain placed on your

body by heat.

• Many energy drinks contain as much

or more sugar as soft drinks, which

adds hundreds of extra calories to

your diet.

Alcohol

• Alcohol can cause dehydration.

• Drinking alcohol within 24 hours of

working in the heat can increase the

risk of heat illness.

What about salt tablets?

NIOSH does not recommend taking salt tablets.

In most cases, salt can be replaced by eating 

normal meals and snacks throughout the day. 

Do not skip meals.

What about caffeine?

The amount of caffeine in tea, coffee, and soft 

drinks probably will not have an effect on 

overall hydration. 

Do I need sports drinks?

In general, eating regular meals with adequate 

water intake is sufficient to maintain water and 

electrolyte balance.

For prolonged sweating lasting several hours, 

sports drinks with balanced electrolytes are 

another option to replace salt lost in sweat.

Heavy consumption of sports drinks will add 

unnecessary calories to your diet due to the 

added sugar.

DEPARTMENT OF HEALTH AND HUMAN SERVICES

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

DHHS (NIOSH) Publication No. 2017-126 

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