The short answer
Cancer treatment can make it easy to become dehydrated, especially with vomiting, diarrhea, or a poor appetite. Sipping fluids through the day, counting soups and other liquids, and watching for signs like dark urine, dizziness, and dry mouth can help. Tell your team if you cannot keep fluids down.
Vomiting, diarrhea, fever, and eating less can all lead to dehydration during treatment.
Sipping fluids steadily through the day is often easier than drinking a lot at once.
Soups, milk, gelatin, ice pops, and watery fruits count toward your fluids.
Signs of dehydration include dark urine, dizziness, dry mouth, and tiredness.
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The full explanation.
Why hydration matters more now
Staying hydrated helps your body handle treatment and clear the byproducts of some medicines. During treatment it can be easy to fall behind on fluids — nausea and a low appetite make drinking harder, while vomiting, diarrhea, or fever make the body lose more. Even mild dehydration can add to fatigue, dizziness, dry mouth, and a bad taste, which can then make eating and drinking even harder.
Easy ways to get enough fluid
Sipping small amounts steadily through the day is usually easier than drinking a lot at once. Keep a drink within reach, and try cool or flavored fluids if plain water is unappealing. All fluids count, not just water: milk, broths and soups, herbal or decaf tea, diluted juice, gelatin, ice pops, and watery fruits and vegetables like melon and cucumber all add up. A general goal often mentioned is around eight cups of fluid a day, but your team may adjust this for you.
Signs of dehydration to watch for
Common signs include dark yellow urine or passing less urine than usual, a dry mouth, feeling thirsty, headache, dizziness (especially standing up), and unusual tiredness. If you are losing fluids through vomiting or diarrhea, you can become dehydrated faster. An oral rehydration drink, which replaces fluid, sugar, and salts, can help in some situations — ask your team whether one is right for you.
When to call your team
Contact your care team if you cannot keep fluids down for several hours, are vomiting a lot or have ongoing diarrhea, notice very little urine, or feel faint or confused. They can look for the cause, adjust medicines, and give fluids into a vein (IV fluids) if needed. Everyone's situation is different. This is general information, not advice for you personally — your care team, and an oncology dietitian if one is available, can tailor it to your treatment.
Words to know
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Common questions
▸How much should I drink during treatment?
A common goal is about eight 8-ounce cups of fluid a day, but the right amount varies. Your team may recommend more if you are vomiting, have diarrhea, or a fever, or less in some medical conditions.
▸Does water have to be plain?
No. All fluids count — soups, milk, decaf tea, diluted juice, gelatin, ice pops, and watery fruits and vegetables. Cool or flavored drinks are often easier during treatment.
▸What are the signs I'm dehydrated?
Dark urine, passing less urine, dry mouth, thirst, headache, dizziness, and tiredness. Losing fluids through vomiting or diarrhea can bring these on faster.
▸When should I call about dehydration?
Call if you cannot keep fluids down, have a lot of vomiting or diarrhea, pass very little urine, or feel faint or confused. Your team can help, including IV fluids.
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