Nutrition and daily life

Fluids and hydration

Drinking enough sounds very simple, but during leukemia treatment it is an important way to protect the kidneys, ease tiredness and constipation, and help the body cope better with medicines. This topic explains how much and what to drink, how to recognise dehydration and which drinks to avoid.

Last updated: 3 October 2026~5 min read

A large translucent water droplet on a dark navy background, with blood cells floating inside it in soft light. — **Figure 1.**Concept: water helps blood flow and cells work.

01Short answer

For most people, drinking regularly through the day helps during treatment, but the right amount is individual: fever, vomiting, diarrhea and hot weather increase the need, while in some heart and kidney conditions the doctor may limit fluids. Your team will tell you your target. Water, weak tea, kompot, soup, milk and pasteurised drinks all count. Water must be safe: if in doubt, drink boiled or sealed bottled water. Grapefruit juice does not mix with some medicines; discuss alcohol, energy drinks and herbal teas with your team first. Thirst, a dry mouth, dark and scanty urine and dizziness are signs of dehydration; if you cannot keep fluids down, call straight away.

02Simple explanation

More than half of the body is water. It helps blood flow, controls temperature and helps the kidneys remove waste in the urine.

During treatment, many medicines and the remains of dying leukemia cells leave the body through the kidneys. Enough fluid helps protect the kidneys.

With fever, vomiting and diarrhea the body loses a lot of fluid. Dehydration can then develop quickly, and you may feel weaker and dizzy.

Fluid is not only water: tea, kompot, soup, milk, yogurt and juicy fruit count too. What matters is that drinks are safe.

There is no single number for everyone. Some people need more fluid, and for others the doctor may set a limit. Check your target with your team.

03Scientific explanation

A general reference: according to the 2010 opinion of the European Food Safety Authority (EFSA), adequate total daily water intake (including water from food) for healthy adults is about 2.0 litres for women and 2.5 litres for men. This is a guide for healthy people; during treatment the need may be higher or lower.

Protecting the kidneys: according to a 2011 review, intravenous fluids and medicines that lower uric acid are used at the start of treatment to prevent tumor lysis syndrome. Some chemotherapy medicines are also given in hospital with extra fluids. Your hematology team plans these fluids.

Losses: according to NCI and Cancer.Net, diarrhea, vomiting and fever are the main causes of dehydration. With diarrhea, oral rehydration solutions from the pharmacy help replace salts and minerals. According to the NHS, early signs of dehydration are thirst, dark yellow strong-smelling urine, passing little urine, dizziness, tiredness and a dry mouth.

Safe water and interactions: according to WHO, contaminated water can be a source of diarrhea and other infections. According to the US FDA, grapefruit juice can change the level of some medicines in the body. This can apply to some targeted leukemia medicines too, so check the leaflet for your medicine.

04What happens in the body?

How much should I drink?

A general rule: drink regularly through the day in small amounts, and aim for urine that is pale straw-coloured. Fever, vomiting, diarrhea, hot weather and activity increase the need. With heart failure, some kidney problems or low blood sodium, the doctor may limit fluids. Your team will tell you your target.

The kidneys and treatment

At the start of treatment, especially when there are many leukemia cells, intravenous fluids may be given in hospital to protect the kidneys. With some medicines, drinking plenty is also advised at home. Your team may ask you to watch the amount and colour of your urine; this shows how well the kidneys are working.

A translucent, glowing kidney shape like a filter on a dark navy background, with a clear teal stream flowing through it. — **Figure 2.**Drinking enough helps the kidneys clear medicine and cell remains.

What can I drink?

Safe water, weak tea, kompot, clear broth, pasteurised milk, yogurt and ayran, pasteurised juices. Ice made from safe water, jelly and juicy fruit such as well-washed watermelon add fluid too. Tea and coffee in moderation are usually fine; keep sugary drinks limited.

What should I avoid?

Alcohol puts strain on the liver, raises the risk of bleeding when platelets are low and can interact with medicines; talk to your team first. Avoid energy drinks, grapefruit and pomelo juice, unpasteurised juices, home-made kvass, and untested well or spring water. Discuss herbal teas with your team first.

Everyday habits

Keep a water bottle where you can see it and wash it every day. Make it a habit to drink a glass with every medicine and every meal. With nausea, cold drinks and small sips are easier. With mouth sores, cool drinks and a straw can help. To protect your sleep, drink most of your fluids during the day.

A row of translucent glasses on a dark navy background, their light shifting from morning to evening. — **Figure 3.**Drinking small amounts through the day is easier.

When to call straight away

If you cannot keep fluids down; you have watery diarrhea 4 or more times in 24 hours; you pass no urine or very little for 8 hours or more; you feel very dizzy on standing, confused or have a racing heart; or you have a fever. These signs may need urgent care.

05How do fluids protect the body?

Drinking enough does several important jobs during treatment.

1Blood flowOxygen and nutrients reach the tissues.

2KidneysMedicine and cell remains leave in the urine.

3Replacing lossesAfter fever, vomiting and diarrhea.

4Daily checksThe colour and amount of urine.

Fluid balanceDehydration is prevented.

Kidney protectionFluids according to your team’s plan.

Urgent signsIf fluids will not stay down, call straight away.

06Drinks: a general guide

Drink	Usually	Note
Safe water	The main choice	If in doubt, boiled or sealed bottled water
Tea, coffee	Fine in moderation	A lot of caffeine can disturb sleep
Kompot, soup	A good choice	Freshly made or stored properly
Milk, yogurt, ayran	Fine	Only from pasteurised or boiled milk
Juices	Pasteurised juices are fine	Grapefruit and pomelo do not mix with some medicines
Alcohol and energy drinks	Not advised	Talk to your team first
Herbal teas	Agree with your team	They may interact with medicines

* This table is general information. Your fluid target and any limits are decided by your hematology team.

07Key terms

Dehydration: Losing too much fluid from the body.
Rehydration solution: A drink with an exact balance of salt and sugar that replaces losses.
Electrolytes: Important minerals in the blood, such as sodium and potassium.
Tumor lysis syndrome: A dangerous change in blood chemistry when many leukemia cells die.
Intravenous fluid: Fluid given into a vein through a drip.
Fluid restriction: A daily fluid limit set by the doctor in some conditions.
Pasteurisation: Heating milk and juices to kill germs.
Interaction: A food or drink changing how a medicine works.

08Key points

Drink regularly through the day, in small amounts.
Pale straw-coloured urine is a good sign.
Fever, vomiting and diarrhea increase the need.
In some conditions the doctor may limit fluids.
Drink only safe water.
Grapefruit juice does not mix with some medicines.
Discuss alcohol and herbal teas with your team.
If fluids will not stay down, call straight away.

09Frequently asked questions

How many glasses a day do I need?

There is no single number for everyone. The need depends on body weight, weather, fever and losses, and how well the heart and kidneys work. Your team will give you the right target.

Can I drink tap water?

It depends on the quality of the water where you live. If in doubt, boil the water or drink sealed bottled water. If you use water filters, change the cartridges on time.

Does tea count as fluid?

Yes, weak tea counts. A lot of strong tea and coffee during the day can disturb sleep, though. Discuss herbal teas with your team first.

What should I drink if I have diarrhea?

Small sips of water, clear broth and rehydration solutions from the pharmacy help replace losses. If you have watery diarrhea 4 or more times in 24 hours, call your team.

Can I have a little wine?

Alcohol is usually not advised during treatment: it puts strain on the liver, can raise the risk of bleeding and can interact with medicines. Talk openly with your team about it.

My child is drinking very little. What can I do?

Bright little cups, a straw, a favourite safe kompot and fruit ice lollies made from safe water can help. If your child has a dry mouth, passes little urine or seems drowsy, call your team.

10Questions for your doctor

Take these questions to your appointment. The ones you save are collected on the “My questions” page and stay on this device only.

How much fluid should I drink each day?
Do I have a fluid limit (for example, because of my heart or kidneys)?
Which signs of dehydration should I watch for?
Which drinks should I avoid?

My questions

12Sources

National Cancer Institute (NCI). Eating Hints: Before, during, and after Cancer Treatment
National Cancer Institute (NCI). Diarrhea and Cancer Treatment
National Cancer Institute (NCI). Constipation and Cancer Treatment
Cancer.Net (ASCO). Dehydration
American Cancer Society. Diarrhea
NHS (UK). Dehydration
World Health Organization (WHO). Drinking-water — fact sheet
World Health Organization (WHO). Five keys to safer food manual
European Food Safety Authority (EFSA), 2010. Scientific Opinion on Dietary reference values for water
U.S. Food and Drug Administration (FDA). Grapefruit Juice and Some Drugs Don’t Mix
Centers for Disease Control and Prevention (CDC). Safer Food Choices for People With Weakened Immune Systems
New England Journal of Medicine, 2011. The tumor lysis syndrome

Medical disclaimerThis information is for educational purposes only and does not replace medical advice.

Last updated: 3 October 2026← Back to the list

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