Boiling is an excellent disinfection method and a poor purification method, and the difference matters. It reliably deals with the biological hazards that make water unsafe in an emergency, and it does nothing about dissolved chemicals and metals except concentrate them slightly as water evaporates. Knowing which problem you have decides whether the kettle is the answer.
What boiling reliably does
Bringing water to a rolling boil inactivates bacteria, viruses and protozoan cysts, including organisms that resist chlorine. That is why a boil water notice is the standard public health response to a suspected contamination event or a main break, and why boiling is the first line for water of uncertain microbiological quality when nothing else is available. A rolling boil for the period the guidance specifies is sufficient, and prolonged boiling adds nothing except evaporation.
What it does not remove, and what it concentrates
Everything dissolved stays behind. Lead, arsenic, nitrate, fluoride, salts and most chemicals are unaffected by heat, and because some water leaves as steam, what remains is very slightly more concentrated than what went in. Boiling water containing lead therefore makes it marginally worse, not better, which is the most important practical consequence of this. Free chlorine does dissipate with a few minutes of boiling, but chloramine largely does not, and neither result is a reason to boil daily.
Where boiling is the right response
During a boil water notice from your utility, in the aftermath of flooding, when using an untested private well or a surface source, and when travelling somewhere the supply is not trusted. In those situations it is fast, needs no equipment and no chemicals, and it works. The EPA notes that 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, so an untested well is a reasonable case for caution.
What to do instead for the other cases
If the concern is a dissolved contaminant found in a test, the equipment has to match the contaminant: reverse osmosis for a broad reduction, adsorptive media for arsenic, a certified filter for lead, ion exchange for hardness. If the concern is a persistent microbiological risk on a well rather than a one off event, ultraviolet or chlorination is the durable answer rather than boiling every glass. Our water softener cost guide covers the hardness case, which boiling makes worse by depositing scale.
Questions people ask about does boiling tap water purify it
Does boiling remove lead?
No. It slightly concentrates it, because water leaves as steam and the lead stays behind. Use a filter certified for lead reduction instead.
How long should water be boiled?
A rolling boil for the period the public health guidance specifies. Boiling for longer achieves nothing beyond evaporation.
Does boiling remove chlorine?
It drives off free chlorine over several minutes, but chloramine largely persists, and neither is a reason to boil drinking water routinely.
Is boiled well water safe to drink?
It addresses the microbiological risk but nothing dissolved. An untested well should be analysed, since chemical contaminants pass through boiling unchanged.