Dehydration Signs and First Aid: What to Do for Adults, Kids and Older Relatives

Quick answer: for mild to moderate dehydration, have the person rest somewhere cool and sip fluids slowly and often, ideally an oral rehydration solution that contains the right balance of salt and sugar. Call 911 or get emergency care if the person is confused, very drowsy, fainting, has a rapid heartbeat or breathing, cannot keep fluids down, has not urinated in many hours, or is a baby with no wet diapers for several hours, sunken eyes or no tears when crying.

This article is part of our emergency first aid guide for city households. It covers how dehydration happens, the warning signs at different ages, how to rehydrate at home, the point at which home care is no longer enough, and what to keep in an apartment so you can manage fluid loss during illness, heat waves and water service interruptions.

Sources: Centers for Disease Control and Prevention (CDC) guidance on heat-related illness and diarrheal illness; World Health Organization (WHO) and UNICEF guidance on oral rehydration salts; American Academy of Pediatrics (AAP) HealthyChildren.org guidance on dehydration in children; MedlinePlus (U.S. National Library of Medicine) information on dehydration. This article is general information and not a substitute for advice from a medical professional.

What Dehydration Is

Dehydration happens when the body loses more water and salts than it takes in. Water makes up a large part of body weight, and it is needed to keep blood volume up, regulate temperature, move nutrients and remove waste. Along with water, the body loses electrolytes such as sodium and potassium, which nerves and muscles need to work properly.

Mild dehydration is common and easy to correct. Severe dehydration is a medical emergency because the body can no longer keep enough blood flowing to vital organs. The goal of first aid is to catch fluid loss early, replace both water and salts, and recognize when a person needs medical treatment such as intravenous fluids.

Common Causes

Most dehydration comes from one of a few sources:

• Vomiting and diarrhea, which are the most common causes of dehydration in young children
• Fever, which increases fluid loss through the skin and breathing
• Heavy sweating during hot weather, exercise or physical work
• Not drinking enough, which can happen when someone is sick, busy, confused or unable to get to water
• Certain medical conditions such as uncontrolled diabetes, which can increase urination
• Some medications, including diuretics, which increase fluid loss through urine

In cities, a few situations come up again and again. Summer heat waves raise indoor temperatures, especially in top-floor apartments without air conditioning. Stomach viruses spread quickly in households, schools and day cares. Water main breaks and boil-water notices can make people drink less without realizing it. Older adults who live alone may not notice thirst or may limit fluids to avoid trips to the bathroom.

Who Is at Higher Risk

Some people become dehydrated faster or have a harder time telling you something is wrong.

Babies and young children

Infants and toddlers have a higher proportion of water in their bodies and lose fluids more quickly with vomiting, diarrhea and fever. They cannot ask for a drink or describe how they feel, so caregivers need to watch for signs such as fewer wet diapers. The AAP notes that young children with vomiting and diarrhea can become dehydrated quickly.

Older adults

The sense of thirst becomes weaker with age, and kidneys become less able to conserve water. Older adults may also take medications that affect fluid balance or have conditions that make it hard to get up and get a drink. The CDC lists older adults among the groups at higher risk for heat-related illness.

People with chronic illness

Diabetes, kidney disease and heart disease can all affect how the body handles fluids. People with these conditions should follow advice from their own health care provider about fluid intake, because some are told to limit fluids.

People working or exercising in heat

Outdoor workers, athletes and anyone doing hard physical work in heat can lose a large amount of sweat in a short time. Dehydration also raises the risk of heat exhaustion and heat stroke.

Signs of Dehydration in Adults

Early signs are easy to miss. Watch for:

• Thirst
• Dry mouth, lips or tongue
• Dark yellow urine or urinating less often
• Fatigue or feeling weak
• Headache
• Dizziness or lightheadedness, especially when standing up

Signs that dehydration is becoming severe include:

• Very little or no urine for many hours
• Confusion, irritability or unusual sleepiness
• Fainting
• Rapid heartbeat or rapid breathing
• Sunken eyes
• Skin that stays tented when pinched and released
• Low blood pressure

Severe dehydration needs emergency care. Do not try to manage it only at home.

Signs of Dehydration in Babies and Children

Children show dehydration differently. Watch for:

• Fewer wet diapers than usual, or no wet diaper for several hours
• No tears when crying
• Dry mouth and tongue
• Sunken eyes
• A sunken soft spot (fontanelle) on top of a baby’s head
• Unusual sleepiness, low energy or fussiness
• Cool, blotchy hands and feet

Call the child’s doctor promptly if a baby under a few months old has vomiting, diarrhea or fever, because young infants can become seriously ill quickly. Call 911 or go to the emergency department if a child is very drowsy, hard to wake, limp, breathing fast, or has not urinated in many hours.

First Aid for Mild to Moderate Dehydration

If the person is awake, alert and able to drink, you can usually start rehydration at home.

1. Move the person somewhere cool and let them rest. Remove extra layers if they are hot.
2. Give small sips of fluid often rather than large amounts at once. Large gulps can trigger more vomiting.
3. Use an oral rehydration solution when vomiting, diarrhea or heavy sweating are involved. These solutions contain sodium, potassium and glucose in amounts designed to help the gut absorb water.
4. Keep going. Rehydration can take several hours. Offer fluids every few minutes and increase the amount as the person tolerates it.
5. Watch for improvement. Signs that rehydration is working include more frequent, lighter-colored urine, less thirst, more energy and less dizziness.

If the person is vomiting, wait a short time after an episode and then start again with very small amounts, such as a teaspoon or a sip every few minutes. Many people can keep down small sips even when larger amounts come right back up.

Why oral rehydration solution matters

Plain water replaces water but not salts. When a lot of fluid has been lost through diarrhea or vomiting, the body also needs sodium and potassium. The WHO and UNICEF oral rehydration salts formula was developed to treat dehydration from diarrhea and is credited with saving many lives worldwide. In the United States, ready-made oral rehydration solutions are sold at pharmacies and grocery stores in liquid, powder and freezer-pop forms.

Sports drinks, sodas and fruit juices are not the same. Many contain a lot of sugar and relatively little sodium, and high sugar drinks can make diarrhea worse in some people. Health organizations generally recommend a commercial oral rehydration solution for children with vomiting or diarrhea.

Feeding during illness

For babies, keep breastfeeding or formula feeding unless a doctor tells you otherwise. Older children and adults can usually return to their normal diet as soon as they feel like eating. Bland foods that are easy to tolerate are fine, but you do not need to keep anyone on a restricted diet for days.

When to Call 911

Call 911 or go to the nearest emergency department if the person:

• Is confused, very drowsy, hard to wake or unresponsive
• Faints or cannot stand without fainting
• Has a rapid heartbeat or rapid breathing
• Has not urinated in eight hours or more (or a baby has no wet diapers for several hours)
• Cannot keep down any fluids
• Has bloody or black stools, or vomit that is bloody or green
• Has severe abdominal pain
• Has signs of heat stroke, such as a very high body temperature with confusion or hot skin

If someone faints, follow our guide to fainting first aid. If the person becomes unresponsive and is not breathing normally, start CPR and use an AED if one is available.

When to Call a Doctor or Nurse Line

Some situations are not emergencies but still need advice from a professional. Call a doctor, telehealth service or nurse advice line if:

• Vomiting or diarrhea lasts more than a day or two in an adult, or less time in a young child
• A baby younger than a few months old has vomiting, diarrhea or a fever
• The person has a chronic condition such as diabetes, kidney disease or heart disease
• The person takes medications that affect fluid levels, such as diuretics
• You are not sure whether home care is working

Many health insurers and hospital systems run free nurse lines that are available around the clock. Write the number down and keep it with your emergency contacts.

Dehydration During Heat Waves

Heat waves are a major cause of dehydration in cities. Buildings hold heat, and apartments on upper floors can stay hot overnight. The CDC recommends drinking more fluids during hot weather regardless of activity level and not waiting until you feel thirsty. It also recommends avoiding very sugary or alcoholic drinks during extreme heat.

Practical steps for apartments:

• Keep a water bottle within reach and refill it on a schedule.
• Check on older neighbors and relatives at least twice a day during a heat wave.
• Spend the hottest part of the day in an air-conditioned place, such as a library or a city cooling center, if your home is hot.
• Keep shades closed on sun-facing windows during the day.
• Avoid using the oven during the hottest hours.

Our guide to extreme heat safety during a heat wave or power outage explains how to plan for hot days when the power goes out.

Dehydration During Stomach Bugs

Stomach viruses such as norovirus spread easily and can cause sudden vomiting and diarrhea. The main danger is fluid loss, especially for young children and older adults. Start oral rehydration early instead of waiting until someone looks dehydrated.

Norovirus is not killed easily by alcohol-based hand sanitizer, so the CDC recommends washing hands with soap and water after using the bathroom and before preparing food, and cleaning contaminated surfaces with a bleach-based cleaner. Keeping the sick person away from food preparation helps protect the rest of the household.

If you suspect the illness came from something you ate, our guide to food poisoning covers warning signs that need medical care.

Planning for Water Outages

Water service interruptions can make it harder to stay hydrated. A water main break may shut off water to your building for hours or days, and a boil-water notice means tap water should not be used for drinking without treatment. FEMA recommends storing at least one gallon of water per person per day for several days, and more for hot climates, pregnant or nursing people and sick people.

For an apartment, that means:

• Store sealed, commercially bottled water and check expiration dates.
• Plan for pets, which also need water.
• Keep a few packets of oral rehydration salts in your first aid supplies.
• Know where the shutoff valve for your unit is in case a pipe breaks.

What to Keep at Home

A few inexpensive items make dehydration easier to manage:

• Oral rehydration solution packets or bottles
• A digital thermometer
• Disposable cups and a medicine syringe or dropper for giving small amounts to young children
• Extra bottled water
• A list of medications for each household member
• Your doctor’s phone number and a nurse line number

Store these with your first aid kit for a small apartment so you can find them quickly during an illness.

Preventing Dehydration Day to Day

Prevention is mostly about habits:

• Drink regularly throughout the day, and more when it is hot or you are active.
• Watch urine color. Pale yellow usually means you are well hydrated.
• Eat foods with high water content, such as fruits, vegetables and soups.
• Take extra fluids when you have a fever, vomiting or diarrhea.
• Make water easy to reach for children and older adults.

Thirst is a useful signal but not a perfect one. Older adults in particular may not feel thirsty even when they need fluids, so a schedule can help.

Common Mistakes

Some well-meaning actions make dehydration worse:

• Giving large amounts of plain water to a baby. Babies under six months generally should not be given plain water unless a doctor advises it. Breast milk or formula and, when recommended, oral rehydration solution are the right fluids.
• Relying on soda or juice to treat diarrhea. High sugar can draw water into the gut.
• Stopping fluids after vomiting. Small, frequent sips usually work better than stopping.
• Waiting too long. Children and older adults can go from mild to severe dehydration faster than you might expect.
• Giving anti-diarrhea medicine to young children without a doctor’s advice. Some of these medicines are not recommended for children.

Frequently Asked Questions

How long does it take to rehydrate after mild dehydration?

Mild dehydration often improves within a few hours of steady fluid intake. Moderate dehydration can take longer. If symptoms do not improve, or if the person gets worse, get medical advice.

Is coconut water good for dehydration?

Coconut water contains potassium but often has less sodium than an oral rehydration solution. It can be part of normal fluid intake, but for dehydration from vomiting or diarrhea, a commercial oral rehydration solution is a better choice.

Can you drink too much water?

Yes. Drinking extreme amounts of water in a short period can lower blood sodium to dangerous levels, a condition called hyponatremia. This is rare in everyday life but can happen during long endurance events. Steady drinking and fluids that contain salts help prevent it.

Are sports drinks the same as oral rehydration solution?

No. Sports drinks are designed for athletes and usually contain more sugar and less sodium than an oral rehydration solution. They are not the best choice for treating dehydration from illness, especially in children.

What color should urine be?

Pale yellow usually means good hydration. Dark yellow or amber urine is a sign to drink more. Some vitamins and medications can change urine color.