Tap water arrives with dissolved minerals, a disinfectant residual and whatever the distribution system contributes on the way. Distilled water has been boiled to steam and condensed back, leaving nearly all of that behind. The practical differences show up in taste, in scale, in cost, and in what each is suited to around the house.
You can find out what is in your tap water
This is the part most people never use. Every community water system publishes an annual Consumer Confidence Report setting out what was detected in the supply over the year, and the EPA maintains a finder to locate yours. Reading it turns the comparison from a guess into a decision: if the report shows nothing you object to, buying distilled water by the jug is solving a problem you do not have. Private well owners get no such report and must test.
Taste, scale and appliances
Tap water's minerals give it the taste people are used to, and also deposit scale in kettles, coffee makers, steam irons and water heaters. Distilled water leaves no deposit at all, which is why appliance manuals often specify it. The same absence makes it taste flat in a glass. So the sensible household split is usually distilled where scale matters and treated tap water where taste matters, rather than switching everything to one or the other.
Cost, weight and effort
Distilled water has to be bought and carried, or made in a countertop still that boils every gallon using electricity and needs its chamber descaled by hand. Tap water arrives under pressure at every fixture with no effort. Over a year the difference is significant in both money and inconvenience, and that alone makes distilled water a poor choice as a household's main drinking supply unless there is a specific reason.
If you are switching because of a problem
Chase the problem rather than the container. A chlorine taste is a carbon filter's job. Scale and slippery soap point at hardness and a softener. A contaminant found on a report or a well test points at a targeted filter or reverse osmosis at the sink. All of those fix the water at the tap, which is cheaper and easier than hauling jugs, and our best tap water in the US guide gives useful context on how supplies vary.
Questions people ask about distilled water vs tap water
Is distilled water healthier than tap water?
Not inherently. It has fewer minerals and fewer contaminants, but treated tap water that meets standards is fine to drink and costs far less.
Can I use tap water where distilled is specified?
In appliances such as steam irons and humidifiers, tap water leaves scale that shortens the appliance's life, which is why the manuals ask for distilled.
How do I know what is in my tap water?
Read your utility's annual Consumer Confidence Report, which the EPA helps you find. On a private well, only a lab test will tell you.