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Nutrition and daily life

Boiling water: how to do it properly

Boiling is the simplest and most reliable way to kill bacteria, viruses and parasites in water, but it must be done properly. Section “Water safety: drinking water, ice and boiling” covered safe water sources; this section is about boiling itself.

Last updated: ~1 min read
A steaming kettle — Boiling water: how to do it properly
Figure 1.A rolling boil — Boiling water: how to do it properly

01Short answer

Bring water to a rolling boil (large, continuous bubbles) and boil for at least 1 minute; at altitude (above about 2,000 m) boil for 3 minutes. An electric kettle that switches itself off usually reaches a rolling boil. Cool it covered in a clean container and use it within 24 hours. Boiling does not remove chemical contaminants such as nitrates or heavy metals. Boiled water can be used for ice, baby food and brushing teeth. Keep the kettle clean and descale it regularly.

02Simple explanation

A rolling boil.

At least 1 minute.

Cool it covered.

Use within 24 hours.

03Scientific explanation

WHO: a rolling boil reliably kills disease-causing organisms in water.

WHO: foodborne illness is more severe in people with weakened immunity; the five keys are keep clean, separate, cook thoroughly, keep food at safe temperatures, and use safe water and raw materials.

04What happens in the body?

A thermos

Keeping boiled water in a thermos is handy for tea.

A covered glass jug.
Figure 2.Cooling water — Boiling water: how to do it properly

Filter plus boiling

A filter improves taste and removes some chemicals; boiling kills germs.

A pot on a gas stove.
Figure 3.Boiling in a pot — Boiling water: how to do it properly

Neutropenia

When neutrophils are low, even ordinary germs can cause serious infection, which is why the rules are stricter.

General rules

This section is part of the general food-safety rules in “Handwashing: the simplest protection” and “Eggs and dairy: safe choices” and “Food safety: four simple rules”.

05Safety: four steps

Check, swap the risky, prepare properly, use in time.

Check — Date and condition.1CheckDate and condition.
Swap — A safe choice.2SwapA safe choice.
Prepare — Clean and thorough.3PrepareClean and thorough.
In time — No delay.4In timeNo delay.
CleanHands and surfaces.
CookGerms die.
ColdGrowth slows.

06Key points at a glance

TopicIn brief
A thermosKeeping boiled water in a thermos is handy for tea.
Filter plus boilingA filter improves taste and removes some chemicals; boiling kills germs.
NeutropeniaWhen neutrophils are low, even ordinary germs can cause serious infection, which is why the rules are stricter.
General rulesThis section is part of the general food-safety rules in “Handwashing: the simplest protection” and “Eggs and dairy: safe choices” and “Food safety: four simple rules”.

07Key terms

Rolling boil
Continuous boiling with large bubbles.
Limescale
A chalky deposit in the kettle.
Foodborne infection
An infection spread through food or water.
Neutropenia
Low neutrophils.

08Key points

  • Boil vigorously.
  • Store covered.
  • Use soon.
  • When in doubt, throw it out.
  • Call if you have a fever.

09Frequently asked questions

Can I boil water in a microwave?

Yes, but heating is uneven and it can boil over suddenly; a kettle is better.

Is reboiling water harmful?

No, usually it is harmless.

Are these rules for ever?

No. They are usually relaxed as blood counts recover; your team will say.

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.

  1. Can I boil water in a microwave?

  2. Is reboiling water harmful?

  3. Are these rules for ever?

My questions

12Sources

  1. World Health Organization. Drinking-water fact sheet
  2. World Health Organization. Five Keys to Safer Food manual
  3. World Health Organization. Food safety fact sheet
  4. U.S. Food and Drug Administration. Safe Food Handling
  5. National Cancer Institute. Eating Hints: Before, During, and After Cancer Treatment
  6. European Food Safety Authority (EFSA), 2010. Scientific Opinion on Dietary reference values for water
  7. National Center for Complementary and Integrative Health (NCCIH). Cancer and Complementary Health Approaches: What You Need To Know
  8. National Center for Complementary and Integrative Health (NCCIH). St. John’s Wort
  9. National Center for Complementary and Integrative Health (NCCIH). Turmeric
  10. American Cancer Society. Dietary Supplements: What Is Safe?
Medical disclaimerThis information is for educational purposes only and does not replace medical advice.
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