To make water safe to drink, bring it to a full, rolling boil and keep it boiling for 1 minute at sea level (or up to about 2,000 meters / 6,500 feet). At higher elevations, boil it for 3 minutes instead.

Standard boiling time (CDC & health agencies)

Most public health authorities, including the U.S. Centers for Disease Control and Prevention (CDC), recommend:

  • At sea level up to 2,000 m (6,500 ft): Bring clear water to a rolling boil, then boil for 1 minute.
  • Above 2,000 m (6,500 ft): Boil for 3 minutes because water boils at a lower temperature at high altitude, so a bit more time is needed to kill all pathogens.

This kills bacteria (like E. coli, Salmonella, Vibrio cholerae), viruses (including hepatitis A), and protozoa (like Giardia and Cryptosporidium) that cause common waterborne illnesses.

What “rolling boil” means

A rolling boil is when big bubbles are rapidly breaking the surface across the whole pot, not just a few small bubbles at the bottom (“fish-eye” stage).

  • Start timing only after the water reaches a full, rolling boil.
  • If the water is cloudy or very dirty, it’s best to filter or let it settle first, then boil the clearer water on top.

When boiling isn’t enough

Boiling kills germs, but it doesn’t remove:

  • Chemical pollutants (like lead, pesticides, or industrial chemicals).
  • Heavy metals or radioactive contaminants.
  • Salt (boiling seawater doesn’t make it drinkable; it just concentrates the salt).

So, if the water is known to be chemically contaminated, boiling alone won’t make it safe; a proper filter or other treatment is needed.

Practical tips for everyday use

  • For a boil-water advisory (city water): Bring tap water to a rolling boil, boil 1 minute (or 3 minutes if above 6,500 ft), then cool and store in a clean, covered container.
  • For camping/backpacking: Filter or strain visibly dirty water first, then boil 1 minute (or 3 minutes at high altitude).
  • For baby formula or very vulnerable people: Follow local health guidance, but usually the same 1‑minute (or 3‑minute) rolling boil is sufficient.

Quick reference table

Situation| Boil time
---|---
Sea level to ~2,000 m (6,500 ft)| 1 minute after rolling boil
Above 2,000 m (6,500 ft)| 3 minutes after rolling boil
Very cloudy/dirty water| Filter/strain first, then boil as above
Seawater or chemically contaminated water| Boiling alone is not enough; use distillation or a proper filter

Information gathered from public forums or data available on the internet and portrayed here.