---
title: "Can you boil water twice? Yes"
description: "Yes. Reboiling is harmless — the claims about concentrated toxins do not survive arithmetic. What actually happens, what goes wrong, and what to do instead."
url: https://atoneplace.net/can-you/boil-water-twice/
site: "At One Place"
---

# Can you boil water twice?

**Yes: Yes. Reboiling is harmless — the claims about concentrated toxins do not survive arithmetic.**

The persistent claim is that reboiling concentrates nitrates, arsenic and fluoride to dangerous levels. Boiling does evaporate some water and does slightly concentrate dissolved minerals, but the amounts involved are tiny: a kettle loses a few per cent of its volume per boil, so concentrations rise by a few per cent, from levels that are already far below any safety threshold in treated drinking water. You would need to boil the same water down to a fraction of its original volume, many times over, for the change to matter at all. What does change is taste — reboiled water has less dissolved oxygen and tastes flatter, which is the real reason tea drinkers prefer fresh water.

## What goes wrong

- No meaningful health risk from ordinary reboiling of treated water.
- The taste flattens noticeably as dissolved gases are driven off.

## Common questions

### Can you boil water twice?

Yes. Reboiling is harmless — the claims about concentrated toxins do not survive arithmetic.

### What happens if you boil water twice?

No meaningful health risk from ordinary reboiling of treated water. The taste flattens noticeably as dissolved gases are driven off.

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## Sources

- World Health Organization — WHO (https://www.who.int/)