Staying hydrated is important every day, but illness can make maintaining fluid balance more difficult. Fever, sweating, vomiting, diarrhea, reduced appetite, and simply feeling too unwell to drink can all increase the risk of dehydration.
This can happen with COVID-19, influenza, stomach illnesses, and many other infections.
Quick answer: During COVID-19 or another illness, drink regularly according to thirst and replace fluids lost through fever, sweating, vomiting, or diarrhea. Water is usually a good choice, while oral rehydration solutions may be useful when significant fluid and electrolyte losses occur. Seek medical care if dehydration becomes significant or you cannot keep fluids down.
In This Guide
Why Hydration Matters
Water is involved in nearly every major body system.
It helps support:
- Normal body temperature
- Blood circulation
- Transport of nutrients
- Digestion
- Kidney function
- Removal of metabolic waste
- Normal cellular function
The human body is made up largely of water, although the exact percentage varies by age, sex, and body composition.
When fluid losses exceed intake, dehydration develops.
How Much Water Do You Need Each Day?
There is no single amount of drinking water that is correct for everyone.
Fluid needs vary with:
- Body size
- Activity level
- Climate
- Diet
- Pregnancy or breastfeeding
- Fever or illness
- Medications
- Kidney or heart conditions
The National Academies established Adequate Intake values for total water of approximately:
- 3.7 liters per day for adult men
- 2.7 liters per day for adult women
These figures include water obtained from all beverages and foods, not just plain drinking water.
These are population-level Adequate Intake values, not mandatory daily drinking targets. Healthy people can maintain normal hydration across a range of water intakes.
I would remove the old “half your body weight in ounces” formula. It sounds precise but does not account adequately for diet, activity, climate, medications, illness, kidney function, or other individual differences.
Common Signs of Dehydration
Possible signs include:
- Thirst
- Dry mouth
- Darker urine
- Urinating less often
- Fatigue
- Dizziness or lightheadedness
- Headache
More serious dehydration can be associated with:
- Confusion
- Marked weakness
- Very little or no urination
- Difficulty remaining alert
- Rapid breathing or heartbeat
Urine color can be a useful clue, but it is not a perfect indicator of hydration. Food, vitamins, medications, kidney function, and other factors can change urine color.
Why Can COVID-19 and Other Illnesses Cause Dehydration?
Respiratory and gastrointestinal illnesses can increase fluid needs in several ways.
Fever
A higher body temperature can increase fluid loss through sweating and breathing.
Reduced Fluid Intake
People who feel sick may drink less because of:
- Fatigue
- Nausea
- Sore throat
- Loss of appetite
- Sleeping more than usual
Vomiting or Diarrhea
These can cause substantial losses of both fluid and electrolytes.
Faster Breathing
Respiratory illness can increase water loss through breathing, especially when breathing becomes faster than normal.
Hospitalized COVID-19 patients have shown both high and low blood-sodium levels in clinical studies. Those electrolyte abnormalities are medically important, but they should not be translated into rigid home instructions about how much water everyone with COVID-19 should drink.
What Should You Drink When You Are Sick?
Plain Water
For many people with mild illness, water is a simple and useful way to maintain hydration.
Other Fluids
Total fluid intake can also include:
- Milk
- Soup or broth
- Seltzer or sparkling water
- Tea
- Other beverages that fit your dietary needs
What About Coffee and Tea?
The original article says tea and coffee can make you more dehydrated. That is too broad.
Caffeinated beverages can have mild diuretic effects, particularly in people who are not accustomed to caffeine, but ordinary amounts still contribute fluid to total daily intake.
If you are ill, large amounts of caffeine may still be undesirable if they worsen:
- Nausea
- Jitteriness
- Sleep problems
- Rapid heartbeat
Alcohol
Alcohol is not a good hydration strategy during illness and may increase fluid loss or interact with medications.
Hydrating Foods Count Too
Food contributes to daily water intake.
Water-rich foods include:
- Watermelon
- Oranges
- Berries
- Cantaloupe
- Peaches
- Cucumber
- Tomatoes
- Celery
- Leafy vegetables
- Soup
- Yogurt
If solid food is difficult to tolerate during illness, soups, broths, and other fluid-rich foods may help provide both fluid and nutrition.
When Are Electrolyte Drinks Useful?
Plain water is adequate for many situations, but significant vomiting, diarrhea, or prolonged sweating can cause losses of sodium and other electrolytes as well as water.
In those situations, an oral rehydration solution may be more appropriate than large quantities of plain water alone.
Oral rehydration solutions contain specific proportions of:
- Water
- Sodium
- Glucose
- Other electrolytes
that help the digestive tract absorb fluid efficiently.
Sports drinks and oral rehydration solutions are not exactly the same thing. Oral rehydration products are specifically formulated for fluid and electrolyte replacement.
Can You Drink Too Much Water?
Yes.
Although uncommon in normal daily life, consuming excessive amounts of water faster than the kidneys can eliminate it can dilute blood sodium.
This condition is called hyponatremia.
Possible symptoms can include:
- Nausea
- Headache
- Confusion
- Weakness
- Muscle cramps
Severe cases can lead to seizures or loss of consciousness.
More water is not always better. There is no benefit to forcing several liters of water over a short period in an attempt to “flush out” COVID-19 or another infection.
Who Is More Vulnerable to Dehydration?
Some people need closer attention during illness.
Older Adults
Older adults may have:
- Reduced thirst sensation
- Lower total body water
- Medications that affect fluid balance
- Mobility problems that make drinks harder to access
See our Dehydration in Older Adults Guide.
Infants and Young Children
Young children can become dehydrated relatively quickly, particularly with vomiting, diarrhea, or fever.
People With Certain Medical Conditions
Fluid needs can require individual medical guidance for people with conditions involving:
- Kidney function
- Heart function
- Liver function
- Fluid restriction
People Taking Certain Medications
Diuretics and some other medications can affect fluid and electrolyte balance.
If a healthcare professional has told you to restrict fluid intake, do not increase it simply because a general hydration article recommends drinking more.
When Should You Seek Medical Care?
CDC lists dehydration among the reasons to seek medical care during a respiratory illness.
Seek appropriate medical attention if you or someone you are caring for:
- Cannot keep fluids down
- Has very little or no urine
- Becomes confused or unusually difficult to wake
- Has persistent or severe dizziness
- Shows signs of significant dehydration
- Has trouble breathing
- Has symptoms that are severe or worsening
People at higher risk of severe COVID-19 or influenza should also contact a healthcare provider promptly because antiviral treatment may be time-sensitive.
Practical Ways to Stay Hydrated When Sick
1. Keep Fluids Within Reach
Keep a glass, cup, or bottle close to where you are resting so drinking does not require much effort.
2. Drink Regularly Rather Than Forcing Large Amounts
Small, frequent amounts can be easier to tolerate, particularly when nausea is present.
3. Use Foods as Part of Hydration
Soup, fruit, yogurt, and other water-rich foods contribute to total water intake.
4. Adjust for Fluid Losses
You may need additional fluid when you are:
- Feverish
- Sweating heavily
- Vomiting
- Experiencing diarrhea
The amount needed varies, so I would not keep the old fixed rule of “500 mL extra per degree of fever.”
5. Consider Oral Rehydration When Necessary
If vomiting or diarrhea is causing significant fluid loss, an oral rehydration product may be more effective than drinking only plain water.
6. Use Flavor if It Helps
If plain water is unappealing, options can include:
- Sparkling water
- Fruit-infused water
- Broth
- Tea
Choose beverages that you tolerate well.
7. Avoid Turning Hydration Into a Competition
You do not need to force water until your urine becomes completely clear.
Very pale urine throughout the entire day can simply mean you are drinking more fluid than necessary.
A practical goal is steady hydration rather than maximum hydration. Pay attention to thirst, fluid losses, urine frequency, how you feel, and any medical guidance that applies to you.
Frequently Asked Questions About Hydration During Illness
Does COVID-19 cause dehydration?
COVID-19 can contribute to dehydration through fever, sweating, reduced fluid intake, vomiting, diarrhea, or increased respiratory water loss. 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. Fluid needs depend on body size, diet, activity, fever, fluid losses, medications, and health conditions. Drink regularly and replace additional losses appropriately.
Should I drink 8 glasses of water every day?
Eight glasses is a simple rule of thumb rather than a universal requirement. Total water needs vary, and water from food and other beverages also counts.
Should I drink half my body weight in ounces?
That formula can provide a rough estimate for some people but should not be treated as a medical requirement. Individual needs vary substantially.
Does coffee dehydrate you?
Normal amounts of caffeinated beverages still contribute to daily fluid intake. Very large amounts of caffeine may have stronger diuretic effects and may be uncomfortable during illness.
Is clear urine a sign of perfect hydration?
Not necessarily. Very pale urine may simply mean high fluid intake. Urine color is only one hydration clue and can be affected by medications, supplements, and health conditions.
Are sports drinks good when sick?
They may provide fluid and electrolytes, but oral rehydration solutions are specifically formulated for dehydration caused by vomiting or diarrhea. Plain water is adequate for many mild illnesses.
Can soup help with hydration?
Yes. Soup and broth contain substantial water and can contribute to fluid intake.
Can you drink too much water?
Yes. Excessive water intake over a short period can dilute blood sodium and cause hyponatremia, which can become dangerous.
Does drinking extra water cure COVID-19?
No. Maintaining hydration supports normal body function but does not cure COVID-19 or eliminate the virus.
When is dehydration serious?
Very low urine output, confusion, marked weakness, inability to keep fluids down, severe dizziness, or other significant symptoms warrant medical evaluation.
Final Thoughts
Hydration is an important part of self-care during COVID-19, influenza, stomach illness, and many other infections.
The most useful principles are simple:
- Drink regularly.
- Replace additional fluid losses.
- Use water-rich foods when helpful.
- Consider oral rehydration when significant vomiting or diarrhea occurs.
- Do not force excessive amounts of plain water.
- Pay attention to signs of dehydration.
- Seek medical care when symptoms become significant.
The goal is normal fluid balance—not drinking as much water as possible. Hydration needs change with illness, activity, temperature, diet, and individual health circumstances.