During a boil water notice, a flood, or a supply failure, boiling is the method public health guidance points to, and it works. It is worth knowing the procedure precisely, because the common errors, boiling too briefly, storing it badly, or assuming it addresses chemical contamination, each undo part of the benefit.
The procedure
Bring the water to a rolling boil, meaning a vigorous boil that does not stop when stirred, and hold it there for the period the guidance in force specifies. Longer than that adds nothing except evaporation. If the water is cloudy, let it settle and filter it through a clean cloth or a coffee filter first, since suspended material both protects organisms and makes the result unpleasant. Let it cool covered rather than uncovered, and use it for drinking, cooking, brushing teeth, washing produce and making ice.
Storing it safely
Boiled water has no disinfectant residual, so it can be recontaminated by a dirty container, unwashed hands or an open jug in a warm kitchen. Store it in clean, covered containers, refrigerate what is not used soon, and discard water that has stood for more than a day or two. Label containers if there is any chance of confusion with untreated water. Flat taste after boiling is dissolved air having left, and pouring the water between two clean containers restores it.
What boiling cannot do
It addresses organisms and nothing else. Lead, arsenic, nitrate, fluoride, salts and most chemicals are unaffected, and because some water leaves as steam, what remains is very slightly more concentrated than what went in. Boiling water that contains lead therefore makes it marginally worse rather than better, which is the single most important thing to know here. If a notice concerns a chemical contamination rather than a microbiological one, boiling is not the response and the guidance will say so.
When a notice is not the situation
The EPA notes private wells are not federally regulated under the Safe Drinking Water Act, and a USGS study of 2,100 private wells found about one in five carried at least one contaminant above a human-health benchmark. On an untested well, boiling handles the microbiological risk while telling you nothing about the chemistry, so it is a stopgap rather than an answer. For a recurring microbiological problem, ultraviolet or chlorination is the durable fix. Our softener cost guide covers the hardness case, which boiling makes worse by depositing scale.
Questions people ask about does boiling water purify it
How long should water be boiled?
To a rolling boil, held for the period the guidance in force specifies. Boiling longer achieves nothing beyond evaporation.
Does boiling remove lead or chemicals?
No. It slightly concentrates them, since water leaves as steam and they remain. Boiling is for organisms only.
How should boiled water be stored?
In clean covered containers, refrigerated, and used within a day or two. It has no disinfectant residual so it can be recontaminated.
Why does boiled water taste flat?
Dissolved air has been driven off. Pouring it between two clean containers restores the taste.