Medical Oncologist
Fluids
How much should you drink during chemotherapy?
Ask your own team for a figure and write it down. Most people on chemotherapy are advised to drink more than usual, commonly somewhere around two to three litres across the day, but that is a starting point rather than a rule. It depends on your size, your drugs and whether you have heart or kidney disease — and with some heart conditions drinking more is actively unsafe.
NG
Medically reviewed by Dr. Naresh GunduConsultant Medical Oncologist · MBBS, DNB (Internal Medicine), DM (Medical Oncology, AIIMS) · last reviewed September 2026, next review due September 2027
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The short answer
How much should you actually be drinking?
Ask your own team for a figure, and write it down. Most people on chemotherapy are advised to drink more than they normally would — commonly somewhere around two to three litres across the day — but that is a starting point rather than a rule, and for some people it would be wrong.
The reason a general number is not enough is that it depends on your size, the weather, which drugs you are having, and whether you have heart or kidney disease. With some heart conditions drinking more is actively unsafe, and with certain treatments your team will ask for considerably more than the usual advice.
The measure that works without a number
Urine. Pale, and passed a normal number of times through the day, means you are keeping up. Dark and scanty means you are not, whatever the glass count says. This is more reliable than any target, and anyone at home can check it.
Ask the question at your next appointment: "How much do you want me drinking?" Then put the answer on the fridge.Why so much
What the extra fluid is actually doing
Several chemotherapy drugs leave the body through the kidneys, and some irritate the bladder and kidneys on the way out. Fluid keeps them moving through rather than sitting in contact with tissue, and it keeps them diluted.
Protecting the kidneys
This is the main reason. Kidney function is checked before most cycles, and if it has fallen, treatment is delayed or the dose reduced. Drinking properly is one of the few things a patient directly controls that affects whether the schedule holds.
Protecting the bladder
With some treatments you may be asked to drink a specific amount and to pass urine frequently, including overnight, because the drug can irritate the bladder lining. If that applies to you it will be explained specifically, and it is worth following exactly.
Everything else it helps
Constipation, which is already being driven by the anti-sickness medicines. Tiredness, which dehydration worsens. A dry mouth, which makes sores and infections more likely. And the ordinary business of feeling well enough to eat.
If you are told to drink a set amount on and around treatment day, that instruction is specific to your drug. Follow it rather than the general advice here.Not sure whether this applies to you?
Ask an oncologistWhat counts
It does not all have to be water
Anything wet counts towards the total. Variety is what makes a larger target achievable.
The everyday options
Plain water, boiled and cooled or bottled. Buttermilk, tender coconut water, thin dal water, rice kanji water and milk. All of these count fully, and several carry a little nutrition as well.
Also counts
- Soups and thin rasam
- Curd and curd rice
- Watery fruit such as melon
When losses are happening
With vomiting or loose motions, oral rehydration solution replaces the salts as well as the water. Mix it exactly as the packet says, and check with your team first if there is heart or kidney disease.
Sports drinks are not the same thing. The balance is different.Work against you
Strong tea and coffee in quantity, because caffeine adds to what goes out. Very sweet packaged juices and fizzy drinks, which can worsen loose motions. Alcohol, which your team will usually ask you to avoid during treatment anyway.
When the mouth is sore
Cool and bland goes down when hot or citrus will not. Buttermilk, cold milk, coconut water and plain cooled water. Ice chips sucked slowly add fluid when even sipping is hard work.
!
One thing that cannot wait
If the person has passed little or no urine since the morning, cannot keep fluids down, or has a fever, do not keep trying at home. Go to the nearest emergency department the same day and say clearly that they are on chemotherapy. The same applies if they are drowsy, confused, or dizzy standing up. Fluid into a vein corrects quickly what is actually dangerous.
Hitting the target
Making a larger amount actually happen
Put it where they are
A bottle beside the chair and another by the bed. Access changes intake far more than intention does. Nobody gets up twelve times a day to fetch a glass from the kitchen.
Sip, do not gulp
Small amounts often stay down better, particularly with sickness, and they leave room for food. A large glass before a meal fills the stomach and the meal gets refused.
Attach it to something
A glass with every medicine, after every trip to the toilet, at the start of every television programme. Habits work better than targets that have to be remembered.
Use the measured bottle
Fill one bottle to the day's amount in the morning and work through it. It removes all the counting and makes the shortfall obvious by evening while there is still time.
Check urine, not the tally
Pale and regular means it is working. If urine is still dark despite hitting the number, say so — that is worth reporting rather than drinking more on your own.
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Being straight with you
What this page cannot tell you
It cannot give you your number. The usual advice suits most people and would be wrong for some, and the situations where it is wrong — heart failure, certain kidney conditions, salts already out of balance — are exactly the ones where getting it wrong matters. Your team has your blood results; a web page does not.
It also cannot tell you whether you are managing. Feeling fine is not evidence, because dehydration during treatment develops quietly. Urine is the practical measure at home, and blood tests are the definitive one.
What to do next
Ask for your figure at the next appointment and write it on the fridge beside the helpline number. Put a bottle where the person actually sits. Watch urine rather than counting glasses. And if it has been scanty today, do not wait until tomorrow to raise it.
Questions we are asked
Common questions about fluids
Is there a standard amount for everyone?
No. The commonly quoted range suits many people and would be unsafe for some, particularly with heart failure or certain kidney conditions. Ask your own team for a figure based on your results and your treatment, and treat any general number as a starting point rather than an instruction.
How do I know if I am drinking enough?
Watch urine rather than counting glasses. Pale, and passed a normal number of times through the day, means you are keeping up. Dark and scanty means you are not, even if you have hit the target. It is the most reliable check available at home.
Do I need to drink more on treatment days?
Often yes, and with some drugs you will be given a specific instruction about the days around the infusion, including passing urine overnight. If you have been told something specific, follow that rather than the general advice, and ask again if you have forgotten the detail.
Can I count tea and coffee?
They contribute in moderate amounts, but relying on them is not a good plan, since caffeine adds to what goes out and strong tea can irritate a sore stomach. Water, buttermilk, coconut water, kanji water and soups are better everyday choices during treatment.
He cuts down to avoid going to the toilet so often. Is that reasonable?
No, and it is a common and harmful decision. Cutting fluids to avoid the toilet is one of the main routes into dehydration and hospital admission during treatment. Solve the toilet access problem instead, and tell the team if urgency is the real issue.
Is it possible to drink too much?
Yes, in some situations. With heart failure, certain kidney conditions, or salts already out of balance, too much fluid causes its own problems. That is precisely why the figure should come from your team rather than from general advice, and why it is worth asking once.
What if drinking makes the sickness worse?
Go smaller and colder — a few sips every ten or fifteen minutes, or ice chips sucked slowly. If nothing is staying down over several hours, stop trying to manage it at home and contact the team, because fluid into a vein resolves it quickly.
Should the whole family be tracking this?
One person should. A rough tally of glasses and of how often urine was passed, on a sheet on the fridge, takes a minute a day. It is the single most useful thing to bring to a clinic or an emergency department, and it turns a vague worry into something that can be acted on.
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Sources
- Cancer Research UK — Cancer drugs side effects
- National Cancer Institute — Nutrition in Cancer Care (PDQ)
- Macmillan Cancer Support — Coping with treatment
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
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