Boiling is an excellent answer to one category of problem and actively counterproductive for another. It kills bacteria, viruses and protozoan cysts reliably, which is why boil water notices exist. It does nothing to dissolved chemical contamination, and because water evaporates while the contaminant does not, boiling concentrates it.
What boiling reliably handles
Microbiological contamination. Bringing water to a rolling boil inactivates bacteria, viruses and the protozoan cysts that resist chlorine, and it needs no equipment, no power supply beyond a stove and no consumables. This is why it is the standard public health instruction after a main break, a flood or a positive coliform result, and why it is the right response to a boil water notice. Cloudy water should be filtered through a cloth or a coffee filter first, since suspended solids shield organisms.
What boiling makes worse
Anything dissolved and not volatile. Nitrate, arsenic, lead, fluoride, most heavy metals and total dissolved solids all remain in the pan while water leaves as steam, so the concentration of the contaminant in what is left goes up rather than down. Boiling water contaminated with nitrate or arsenic and then drinking it delivers more of the contaminant, not less, and this is a genuinely dangerous misunderstanding rather than merely an ineffective one. Those contaminants need reverse osmosis, distillation or a specific adsorptive media.
The awkward middle ground
Some things are partly driven off. Chlorine largely evaporates with a few minutes of boiling, which is why boiled water tastes flatter and less chemical, and volatile organic compounds behave similarly, though a lidded pan simply condenses them back. Hardness partly precipitates as scale in the kettle, which is why the kettle furs, but the water that comes out is not softened in any useful sense. Treat none of these as a treatment method: they are side effects of boiling rather than reasons to do it.
When boiling is the right tool
During a boil water notice, after flooding, after work on a well or the mains, and while awaiting a bacteriological result. It is not a standing arrangement: the EPA notes private wells are not federally regulated under the Safe Drinking Water Act, so a well with recurring coliform contamination needs its wellhead corrected and then ultraviolet or chlorination, not a permanent routine at the stove. Boiled water should also be stored covered and used within a day, since it can be recontaminated on standing.
Questions people ask about does boiling tap water make it safe to drink
Does boiling remove lead or arsenic?
No, and it makes them worse. Water leaves as steam while the contaminant stays, so the concentration in what remains increases.
How long should water be boiled?
A rolling boil is what public health guidance specifies. Filter cloudy water through a cloth first, since suspended solids shield organisms.
Does boiling soften water?
Not usefully. Some hardness precipitates as kettle scale, but the water that comes out is not softened in any meaningful sense.
Can I rely on boiling long term?
No. A well with recurring contamination needs the wellhead corrected and then ultraviolet or chlorination, not a permanent routine at the stove.