Why Plain Water Is Not Always the Best Drink in Extreme Heat

For people working outdoors or in hot environments, staying hydrated is one of the most important ways to prevent heat illness.

But plain water may not always be the drink that keeps the body hydrated the longest.

A University of St. Andrews study published in the American Journal of Clinical Nutrition compared 13 common beverages and found that milk and oral rehydration solutions helped the body retain more fluid than water.

Researchers found that those drinks produced about 25% less urine than plain water. The difference appears to come from ingredients such as sodium and small amounts of sugar, which help slow the movement of fluid through the stomach and improve absorption.

That does not mean workers should stop drinking water.

For shorter periods of work in the heat, cool water is usually enough. The most important rule is to begin drinking before thirst becomes strong.

The Occupational Safety and Health Administration advises workers in hot conditions to drink about one cup of water every 15 to 20 minutes.

During heavy work that produces a great deal of sweat, total fluid intake may reach 32 ounces per hour.

The water should be cool, generally around 50 to 60 degrees, and easy to reach. Workers are less likely to drink enough when water is warm, far away, or available only during scheduled breaks.

Longer shifts require greater attention to electrolyte balance.

OSHA recommends adding electrolyte drinks during jobs lasting more than two hours, especially when workers are sweating heavily.

Sweat removes more than water. It also carries sodium, potassium, and other minerals needed for muscles and nerves to work properly.

Losing too much sodium can contribute to cramps, weakness, nausea, confusion, and more serious heat illness.

Electrolyte drinks can help replace those minerals, but workers should choose them carefully. Drinks with very high sugar levels may upset the stomach or add unnecessary calories, while energy drinks containing large amounts of caffeine are not a substitute for proper hydration.

Milk may help the body retain fluid, but it is not always practical during strenuous outdoor work. For most workers, the simplest plan is cool water for shorter tasks and a balanced electrolyte drink when heat exposure and sweating continue for several hours.

Hydration is only one part of heat safety.

Workers also need shaded or cooled rest areas, regular breaks, lightweight clothing, and time to gradually adjust to hot conditions. New workers and those returning after time away are at greater risk because their bodies have not yet adapted.

Warning signs such as dizziness, headache, confusion, vomiting, fainting, or stopped sweating should never be ignored.

The best drink depends on how long and how hard someone is working.

Plain water remains essential, but during long, sweaty shifts, replacing lost electrolytes can help the body hold onto that water and keep working safely.