Hydration in Heatwaves: Practical Guidance for Vulnerable Groups

During heatwaves, the key to safety is not just “drinking more” but drinking wisely. That means the right total amount of fluid, taken in small, frequent portions, at a comfortable cool (not ice‑cold) temperature, combined with sensible limits on physical activity in the heat. Electrolyte drinks and oral rehydration solutions are useful tools in specific situations—heavy sweating, prolonged outdoor work, or illness—but they sit within a broader sequence of protective actions: water quantity, drinking pattern, food choices, and activity planning.

1. Who is most vulnerable in heat?

Certain groups are more likely to suffer dehydration, heat exhaustion, or heatstroke:

• Older adults, especially over 65, and people living alone.

• Individuals with heart, lung, kidney disease, diabetes, or neurological conditions.

• Pregnant women, infants, and very young children.

• People on medications that affect fluids or blood pressure (diuretics, some antidepressants, antipsychotics).

• Outdoor workers, athletes, and caregivers who spend long periods in the sun.

For these groups, heat safety should be planned in advance—especially on days when they will spend time outside cooled spaces.

2. Drinking wisely: how, how much, and what

Total amount. Most adults in hot weather should aim for around 2–2.5 liters of fluid per day, unless they have medical limits on fluid intake. Rather than counting precisely, encourage people to use thirst, urine colour, and how they feel (energy, dizziness) as simple guides.

Pattern of drinking. Small, frequent portions are safer and more effective than large, infrequent volumes. For example, one glass (100–150 ml) every hour while awake works better than rarely drinking and then “catching up” with a big bottle.

Water temperature. Cool or room‑temperature water is ideal. Very ice‑cold drinks can cause discomfort, and in some frail people may briefly stress the cardiovascular system, so “pleasantly cool” is a good target.

Food as hydration. Fruits (melon, oranges, berries), salads, soups, yoghurt, and lightly cooked vegetables provide water plus natural electrolytes like potassium and magnesium. For many older adults, a bowl of soup or fruit salad may be easier than drinking an extra glass of water.

Electrolytes: targeted, not routine.
Electrolyte drinks and oral rehydration solutions are most useful when:

• Someone is sweating heavily for prolonged periods (outdoor workers, athletes).

• There is vomiting or diarrhoea.

• A person has been in the heat for several hours and is clearly fatigued and depleted.

They are not automatically needed for every healthy adult on a hot day. For people with heart or kidney disease or those on strict low‑salt diets, use them only on medical advice.

3. Temperature bands and practical advice (outside cooled spaces)

These steps apply when people spend time outdoors or move frequently between cooled and hot environments.

Up to 26 °C

• Encourage regular drinking: small glasses across the day, especially for older adults.

• Include water‑rich foods in meals and snacks.

• Use light clothing and short breaks in shade during outdoor activities.

Around 30 °C

• Increase fluid intake towards 2–2.5 liters for adults, if tolerated.

• Plan outdoor errands for morning or evening; limit midday exposure for vulnerable groups.

• Caregivers and outdoor workers should take short “micro‑breaks” in shade to drink and rest.

32 °C

• Make hydration more structured: for example, a drink every 45–60 minutes when outdoors.

• Encourage cool showers or wet cloths on neck and arms after returning from heat.

• Outdoor workers doing moderate exertion may consider one electrolyte or ORS drink during a long shift, alongside plenty of plain water.

34 °C

• Vulnerable groups (older adults, pregnant women, people with chronic conditions) should avoid intense outdoor activity; essential tasks should be brief and well‑timed.

• Outdoor workers should reduce workload intensity, increase rest breaks, and ensure shaded or cooler rest areas.

• Hydration plan: frequent small drinks, water‑rich snacks, and, for those sweating heavily, carefully chosen electrolyte or ORS use.

36 °C and above

• Treat the heat as potentially dangerous, especially for vulnerable people.

• Limit outdoor time to the shortest necessary periods; use hats, light long sleeves, and shade.

• Hydration becomes urgent: very frequent small sips of water, cooling measures, and close monitoring for dizziness, confusion, racing heart, or very dark urine—signals to seek urgent medical help.

4. Everyday routines for vulnerable groups

For older adults and people with chronic illness:

• Keep a visible jug or bottle and small glass nearby to prompt regular drinking.

• Combine fluids with meals and medications to build hydration into routine.

• Encourage light, cool foods and limit alcohol, which dehydrates.

For pregnant women and children:

• Offer water regularly; children often forget to drink when playing.

• Use fruits and yoghurt as appealing, hydrating snacks.

• Avoid high‑caffeine energy drinks; they can worsen dehydration and strain the heart.

For outdoor workers and caregivers:

• Use structured schedules: planned breaks, planned drinks, and planned shade.

• Treat electrolytes as a tool for long, sweaty work—never as a replacement for water or rest.

• Watch colleagues and clients for signs of overheating; early recognition prevents emergencies.

Hydration in heatwaves is a sequence, not a single action: smart drinking, suitable foods, sensible pacing of outdoor activity, and, where needed, cautious use of electrolyte solutions. For vulnerable groups, this combination turns a dangerous day into a manageable one.

You can learn more by reading our e-book 

Mykola Iabluchanskyi together with Andriy Yabluchanskiy