Fever, sweating, vomiting, diarrhea, reduced appetite, and simply feeling too unwell to drink can make dehydration more likely during COVID-19 and many other illnesses. Mild dehydration may improve with regular fluid intake, but significant dehydration can require medical care.
Quick answer: Take small, regular drinks and replace additional fluid losses. Plain water is suitable for many mild illnesses. An oral rehydration solution may be more appropriate when vomiting or diarrhea causes substantial fluid and electrolyte loss. Seek care if fluids will not stay down, urine output becomes very low, or confusion, breathing difficulty, or other severe symptoms develop.
Thirst, dry mouth, darker urine, less frequent urination, fatigue, or lightheadedness.
Use frequent, tolerable amounts instead of forcing large volumes at once.
Very little urine, confusion, inability to drink, severe weakness, or breathing difficulty needs prompt attention.
Why Illness Can Cause Dehydration
Dehydration develops when fluid losses exceed fluid intake. Illness can affect both sides of that balance: it may increase the amount of fluid leaving the body while making it harder to drink enough.
Fever and Sweating
A higher body temperature and sweating can increase fluid loss. Someone who is resting under heavy bedding or in a warm room may lose additional fluid without noticing how much.
Vomiting and Diarrhea
Vomiting and loose stools remove both water and electrolytes. Repeated episodes can cause dehydration relatively quickly, especially in infants, young children, older adults, and people who were already drinking poorly.
Reduced Intake
Nausea, sore throat, altered taste, fatigue, loss of appetite, and sleeping more than usual can all reduce fluid intake. A person may become dehydrated even without obvious sweating or digestive symptoms if they drink very little for an extended period.
Faster Breathing
Breathing releases water vapor. Faster breathing can increase this loss, although breathing difficulty is also a warning sign that should not be managed simply by drinking more water.
Signs of Dehydration During Illness
Dehydration exists on a spectrum. No single sign proves how dehydrated someone is, so look at the overall pattern and whether symptoms are worsening.
| Possible Early Signs | Concerning Signs | Additional Signs in Infants and Children |
|---|---|---|
| Thirst or dry mouth | Very little or no urination | Fewer wet diapers or no urine for an extended period |
| Darker urine | Confusion or unusual difficulty staying alert | Dry mouth or no tears when crying |
| Urinating less often | Fainting or severe, persistent dizziness | Sunken eyes or a sunken soft spot in an infant |
| Fatigue or headache | Rapid heartbeat, marked weakness, or worsening condition | Unusual sleepiness, irritability, or poor interaction |
The National Institute of Diabetes and Digestive and Kidney Diseases lists extreme thirst or dry mouth, reduced urination, fatigue, dizziness, dark urine, and sunken eyes or cheeks among possible dehydration signs.
Urine color is only one clue. Food, supplements, medications, and health conditions can change urine color. Completely clear urine is not a goal that requires continually drinking more water.
What Should You Drink When You Are Sick?
Plain Water
Water is an appropriate first choice for many people with a mild illness who are eating normally and are not losing large amounts of fluid through vomiting, diarrhea, or heavy sweating.
Broth, Soup, and Other Fluids
Broth, soup, milk, tea, diluted juice, sparkling water, and other tolerated beverages can contribute to total fluid intake. Water-rich foods such as fruit, yogurt, and soup also count.
Coffee and Tea
Ordinary amounts of caffeinated beverages still contribute fluid. During illness, however, large amounts of caffeine may worsen nausea, jitteriness, sleep problems, or a racing heartbeat. Choose what you tolerate comfortably.
Alcohol
Alcohol is not a hydration strategy and may worsen fluid loss, impair judgment, or interact with medications. It is best avoided while acutely ill.
When Are Oral Rehydration Solutions Useful?
Vomiting, diarrhea, and prolonged heavy sweating remove electrolytes as well as water. An oral rehydration solution contains water, glucose, sodium, and other electrolytes in proportions designed to support fluid absorption.
According to NIDDK treatment guidance, small sips can be easier to tolerate when vomiting is a problem. Oral rehydration products are particularly worth discussing for:
- Repeated vomiting or diarrhea
- Older adults
- People with signs of dehydration
- People whose medical conditions increase the consequences of fluid loss
- Children, using age-appropriate guidance from a healthcare professional
Sports drinks and oral rehydration solutions are not identical. Sports drinks are formulated primarily for exercise, while oral rehydration products use a more specific balance of glucose and electrolytes for fluid replacement. For infants and young children, ask a healthcare professional which product and amount to use.
How Much Fluid Should You Drink?
There is no single COVID-specific or illness-specific amount that is correct for everyone. Fluid needs vary with body size, diet, fever, sweating, vomiting, diarrhea, pregnancy, breastfeeding, medications, climate, and medical conditions.
Population-level water-intake estimates include water from all foods and beverages; they are not instructions to drink that amount as plain water. During an illness, it is usually more useful to consider:
- Whether you are thirsty
- Whether you are urinating at a reasonably normal frequency
- Whether vomiting or diarrhea is continuing
- Whether small drinks remain down
- Whether dizziness, weakness, or alertness is improving or worsening
- Whether a clinician has given you a fluid target or restriction
For nausea or vomiting, start with small, frequent sips rather than a full glass at once. If fluids repeatedly come back up or intake remains inadequate, contact a healthcare professional.
Can You Drink Too Much Water?
Yes. Excessive water intake over a short time can dilute blood sodium and contribute to hyponatremia. Possible symptoms include nausea, headache, confusion, weakness, muscle cramps, seizures, or loss of consciousness.
More is not always better. Forcing several liters of water does not “flush out” COVID-19 or another illness. The goal is replacing reasonable losses and maintaining fluid balance—not drinking the maximum amount possible.
Who Needs Extra Caution?
They can lose fluid quickly and cannot always communicate thirst or obtain a drink themselves.
Thirst sensation may be reduced, and mobility, memory, medications, or chronic conditions may complicate hydration.
Vomiting, diarrhea, fever, or reduced intake should be discussed promptly when dehydration is developing.
They may need individualized fluid and electrolyte guidance rather than general advice to drink more.
Diuretics and other medicines may affect fluid balance or require professional guidance during illness.
Contact a healthcare professional promptly because treatment may be time-sensitive.
For more age-specific information, see our Dehydration in Older Adults Guide.
If you have been told to limit fluids or sodium, follow that medical plan. Do not increase water or electrolyte drinks simply because a general article recommends hydration during illness.
When to Contact a Healthcare Professional
Contact a healthcare professional promptly when:
- You cannot drink enough or repeatedly vomit fluids
- Vomiting or diarrhea is persistent, severe, or worsening
- Urination is much less frequent than usual
- Dizziness, weakness, or dehydration signs are not improving
- An infant, young child, older adult, or medically vulnerable person is drinking poorly
- You have questions about an oral rehydration product, medication, or fluid restriction
- You are at higher risk of severe COVID-19 and may benefit from time-sensitive treatment
Seek Urgent Medical Care for Severe Warning Signs
Seek urgent medical care for symptoms such as:
- Difficulty breathing or shortness of breath
- Persistent chest pain or pressure
- New confusion, fainting, or inability to stay awake
- Bluish, gray, or unusually pale lips, skin, or nail beds
- Seizure
- Very little or no urine with marked weakness or worsening illness
The CDC's respiratory-illness guidance includes breathing difficulty, persistent chest symptoms, confusion, inability to wake, and dehydration among warning signs that require urgent attention.
Symptoms can change quickly during an illness.
Review Current CDC Warning SignsPractical Hydration Tips During Illness
- Keep a drink within reach. Place a cup or bottle beside the bed or chair where you are resting.
- Use small, frequent amounts. Sips may be easier than a full glass when nausea or sore throat is present.
- Choose fluids you tolerate. Water, broth, soup, tea, diluted juice, or an appropriate oral rehydration product may be options.
- Include water-rich foods. Soup, yogurt, fruit, gelatin, and similar foods can contribute fluid when solid meals are difficult.
- Track the overall pattern. Notice urination, ongoing losses, alertness, and whether symptoms are improving.
- Ask someone to check in. This is especially helpful for an older adult, a person living alone, or anyone feeling unusually weak.
- Do not wait for severe dehydration. Seek professional guidance when intake is falling behind ongoing losses.
Does Filtered Water Help During Illness?
Filtered water does not treat COVID-19, cure an illness, or correct significant dehydration by itself. Its practical value is simply that water with a preferred taste or odor may be easier for some people to drink regularly.
Use and maintain any household filter according to its instructions. When vomiting or diarrhea has caused meaningful electrolyte loss, plain filtered water may not replace everything that has been lost; an appropriate oral rehydration product or medical care may be needed.
Berkey® claim guidance: A Berkey® system can provide convenient countertop filtered water, but it should not be promoted as treating COVID-19, preventing dehydration-related complications, or providing the same function as an oral rehydration solution.
Frequently Asked Questions
Can COVID-19 cause dehydration?
It can contribute to dehydration through fever, sweating, reduced intake, vomiting, diarrhea, or faster breathing. Not everyone with COVID-19 becomes dehydrated.
How much water should I drink when I have COVID-19?
There is no universal COVID-specific amount. Drink regularly, replace additional losses, and consider your diet, medications, medical conditions, and any clinician-provided instructions. Do not force large amounts at once.
What is the best drink when vomiting?
Small, frequent sips are often easier to keep down. An oral rehydration solution may be useful when vomiting causes significant fluid and electrolyte loss. Persistent inability to retain fluids requires medical advice.
Is an electrolyte drink always necessary?
No. Plain water and a normal diet are sufficient for many mild illnesses. Electrolyte replacement becomes more relevant with repeated vomiting, diarrhea, prolonged heavy sweating, or signs of dehydration.
Are sports drinks the same as oral rehydration solutions?
No. Oral rehydration products use a specific balance of glucose and electrolytes. Sports drinks are formulated for exercise and can contain a different sugar and sodium balance.
Does coffee dehydrate you?
Ordinary amounts still contribute fluid, although large amounts of caffeine may be uncomfortable during illness or worsen certain symptoms.
Is clear urine proof of ideal hydration?
No. Urine color is only one clue, and completely clear urine can reflect more fluid intake than necessary. Medications, foods, and supplements can also change its color.
How can I tell whether a child is dehydrated?
Possible signs include fewer wet diapers or less urination, dry mouth, no tears when crying, sunken eyes, unusual sleepiness or irritability, and poor fluid intake. Children can worsen quickly, so contact a healthcare professional when concerned.
Can drinking too much water be harmful?
Yes. Excessive intake over a short time can dilute blood sodium. Headache, nausea, confusion, weakness, seizures, or loss of consciousness after very high fluid intake requires urgent medical evaluation.
Does drinking extra water cure COVID-19?
No. Maintaining fluid balance supports normal body function but does not cure COVID-19. People at higher risk should contact a healthcare professional promptly because treatment may be time-sensitive.
Final Thoughts
Good hydration during illness means keeping fluid intake reasonably matched to losses—not drinking as much water as possible. Use small, regular amounts, choose fluids you tolerate, and consider oral rehydration when vomiting or diarrhea causes meaningful electrolyte loss.
Pay particular attention to infants, children, older adults, people with chronic medical conditions, and anyone who cannot keep fluids down. Very low urine output, confusion, severe weakness, breathing difficulty, or a rapidly worsening condition should not be managed at home with water alone.
Medical notice: This article provides general educational information and does not replace individualized advice, diagnosis, or treatment from a qualified healthcare professional.