Understanding Hydration in Children

By: Dr. Michelle MD

All living things are mostly water. About 90% of our body weight is water. We need water to survive. Putting fluids into the body is known as hydration. We lose water from three mechanisms in our physiology: respiration (the fog on the mirror when we breathe on it), insensible water loss from sweat, and elimination via urination or defecation. Dehydration occurs when the losses are greater than the input.


On the whole, we usually maintain our normal water balance by eating and drinking. All fruits and vegetables, all protein foods, and all cooked starches are mostly water in their composition. All the liquids we drink are water. In normal circumstances, we replace the water lost from sweat, respiration, and elimination, so the body stays healthy and well hydrated.


There are several problems that can arise that can cause more fluid to leave the body than enters it. When this happens, dehydration is the result.

  • Heat Problems including fever, exertion or extreme heat, causing excessive sweating

  • Vomiting, causing an inability to keep fluids that are taken in

  • Diarrhea, causing excessive loss of water from the bowels

  • Diabetes mellitus, causing excessive urination



Thirst is a good mechanism to remind us to drink. In a normal, healthy person, there is almost never a problem with dehydration if adequate fluids are available. There is really no need to drink more than we are thirsty for. It is important to note that healthy babies (who cannot yet talk) must be offered fluids on a regular basis, especially in hot weather. Infants should be offered a mother’s milk or formula, not water or juice, since they need nutrition, and drinking is their only source. Water is a great drink selection for all children above nine months. The juice is really just sugar water, so it should be used sparingly on a day-to-day basis.


Signs of adequate hydration and dehydration

How can we tell if the child is adequately hydrated? A well-hydrated child is alert, has a shiny wet tongue, cries with an appropriate amount of tears, and urinates regularly. The urine is light in color.


If there is a deficit of fluid, the urine output decreases dramatically, and the child gets lethargic and irritable. The tongue gets pasty, and the saliva gets thick and stringy, the eyes look dull and sunken, and there are no tears when crying. The urine, when it is present, becomes dark yellow to orange and has a strong odor. These changes occur gradually as the condition worsens. (One exception: In children with diabetes, paradoxically, the urine output remains high while the child develops all of the signs of dehydration.)


Older children will complain of headaches, nausea, and weakness when they are in the early stages of dehydration.


Preventing Dehydration

Heat problems

During high fever, or in very hot weather and during exertion, the fluid loss is mainly from sweat, and it is important to give extra fluids. When there is high fever, the body can be cooled by tepid bathing or giving antipyretics such as acetaminophen and ibuprofen. Reducing the body temperature to normal or near-normal will decrease the loss of fluids. Water sports like sprinkler running, water fights, and swimming activities are good. Allowing a child to run around in wet clothes on these days helps prevent dehydration.


During very hot weather, especially during exertion in hot weather, the most important precaution is to drink often and replace salt as well as fluid. Sweat, which is needed to keep the body from overheating, is made up of salt and water. In the circumstance of hot weather and exertion, replacing only water can lead to a salt deficiency, which can cause serious imbalances in the body’s chemistry.


I usually recommend that children be given lots of water and small amounts of pretzels, pickles, or other salty foods. There are drinks that are sold, like Powerade, which have some salt in them, but there is not enough salt to make them worth all the junk in them. Ordinary tap water, which can be conveniently carried in sports bottles, is the most refreshing drink and the best hydrator.



There are many illnesses that a child can contract, which leads to vomiting. Vomiting can cause dehydration by preventing the entry of fluids into the body. Overcoming vomiting in a child with viral gastroenteritis can be very challenging. One useful trick is to give very small amounts of fluids at a time. We usually advise parents to start with ½ ounce of a clear liquid every 15 minutes for one hour, and if it is tolerated without vomiting, increase the amount by ½ ounce every 15 to 20 minutes. If the child vomits, wait 30 minutes and try the last volume that was tolerated.


It is advisable to have some sugar in the clear liquids, to take away the Ketones which form during starvation. Ketones can add to the feeling of illness and increase nausea. Even sugar or lollipops can help this part of the problem.


Infants do well with mother’s milk as the fluid, but not with formula. For non-nursing infants and children under 18 months, we usually use the rehydration solution, Pedialyte. This clear liquid, which also comes in ice pops, has the replacement sugar, salt, and fluid needed to maintain the body chemistry. Older children can drink any clear drink or nibble on regular ice pops. The artificial orange ones seem to allay nausea best. White grape juice is less acidic than apple juice, so it is better tolerated. Clear chicken broth, the age-old remedy, actually works fine. If the vomiting does not abate, and the child shows signs of dehydration, a physician should be contacted. Intravenous hydration may be needed.



When there is a diarrhea present, the loss of water can usually be replaced by oral intake. Once vomiting has stopped, the fluids can be given in any quantity the child will take. At this point, the child should be given a full solid food diet, including milk and milk products. This will increase the number of bowel movements initially, but it will ultimately stop diarrhea most efficiently. Probiotics such as Culturelle and Florastor are very useful in stopping diarrhea.


If the diarrhea is severe and watery, and if the child shows signs of dehydration, a physician should be contacted.


Diabetes Mellitus

This is very rare in children, but when it occurs, the child has an excessive thirst, urination, and weight loss, and appears dehydrated despite the large urine output. If this is suspected, a physician should be contacted. Maintaining hydration is a very important job. It is very helpful to monitor children during the course of a potentially dehydrating illness so that hydration can be increased whenever signs of dehydration are noted. As in many other situations, prevention is the best cure, so staying ahead of the fluid requirements on a hot day saves a lot of problems.

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