Tap water and distilled water differ in one fundamental way: what’s dissolved in them. Tap water contains minerals, trace metals, fluoride, and disinfectants picked up during treatment and delivery. Distilled water has had virtually everything removed through evaporation, leaving less than 1 part per million of total dissolved solids. That single difference creates a cascade of practical distinctions in taste, pH, health effects, and appropriate uses.
How Each Type Is Produced
Municipal tap water goes through a multi-step treatment process. Water utilities filter out sediment, kill bacteria with chlorine or similar disinfectants, and in most U.S. systems add fluoride for dental health. The finished product then travels through miles of pipes before reaching your faucet, picking up small amounts of copper, lead, or other metals from the plumbing along the way. The EPA sets legal limits for over 90 contaminants in public water systems, including a maximum of 0.010 mg/L for arsenic and an action level of 0.010 mg/L for lead.
Distillation works differently. Water is heated until it becomes steam, leaving behind dissolved minerals, metals, nitrates, and most bacteria. The steam then cools and condenses back into liquid. Because inorganic compounds and large organic molecules don’t evaporate, they stay behind in the boiling chamber. The result is water with a total dissolved solids (TDS) reading under 1 ppm, compared to tap water where TDS up to 600 mg/L is considered normal and palatable.
Mineral Content
Tap water carries measurable amounts of calcium, magnesium, sodium, copper, and other minerals. A USDA analysis of U.S. municipal water found that two liters of tap water (roughly a day’s drinking) supplies about 6% of recommended calcium intake, 5% of magnesium, 10% of copper, and 3% of sodium. Those numbers vary widely by location. In areas with hard water, the same volume could provide up to 20% of daily calcium and 23% of magnesium needs.
Distilled water contains none of these minerals. On its own, that gap is small enough that a balanced diet can compensate. But the concern grows when distilled or other demineralized water is used for cooking. Research published in the Medical Journal of the Armed Forces India found that cooking with low-mineral water can pull essential elements out of vegetables, meat, and grains, with losses reaching 60% for magnesium and calcium, 66% for copper, and as high as 86% for cobalt. Cooking with mineral-rich hard water, by contrast, causes far less nutrient loss and can even increase the calcium content of food.
pH and Taste
Tap water typically has a pH around 7.5, which is slightly alkaline. Distilled water starts out neutral at 7.0 but quickly drops to about 5.7 once exposed to air. It absorbs carbon dioxide, which forms traces of carbonic acid and pushes the pH into mildly acidic territory. This isn’t dangerous to drink, but it does affect how the water tastes.
Most people describe distilled water as flat or empty. That’s because the minerals dissolved in tap water are what give it flavor. Health Canada uses distilled water as the “tasteless” baseline in formal water-taste research. The dissolved calcium, magnesium, sodium, and their associated compounds in tap water each contribute subtle salty, sweet, or bitter notes. Taste thresholds for these minerals start around 30 mg/L for sodium and roughly 100 to 125 mg/L for magnesium and calcium. Since most tap water contains these minerals well below those thresholds, the flavor is mild, but it’s enough to make tap water taste noticeably different from distilled.
Fluoride and Dental Health
Most U.S. municipal water systems add fluoride at 0.7 mg/L, the level the CDC identifies as effective for cavity prevention. Distilled water contains no fluoride, or only trace amounts, unless it’s specifically added back in. The CDC notes that people who drink mostly purified, distilled, or demineralized water may not get enough fluoride to protect their teeth. If you’ve switched entirely to distilled water for drinking, it’s worth factoring that into your dental care routine.
Long-Term Health Considerations
Drinking distilled water occasionally is perfectly safe. The question is what happens when it replaces mineralized water over months or years. A body of epidemiological research links long-term consumption of demineralized or very soft water to several health concerns. Studies have associated low-calcium water with a higher risk of bone fractures in children, and low-magnesium water with increased risk of cardiovascular disease, certain pregnancy complications like preeclampsia, and some types of cancer. An expert consensus group concluded that the protective effect of hard water on heart health is likely real, with magnesium as the main contributor.
These findings don’t mean a glass of distilled water is harmful. They reflect patterns seen in populations whose primary water source lacked minerals over long periods. If your diet is rich in leafy greens, nuts, dairy, and other mineral-dense foods, you can offset what’s missing from the water. But researchers have noted that even in industrialized countries with good diets, food alone may not fully compensate for the absence of magnesium in drinking water.
When Distilled Water Is the Better Choice
Distilled water isn’t meant to compete with tap water at the dinner table. Its real value is in situations where mineral content causes problems. CPAP machines are a common example. Tap water leaves mineral deposits in the humidifier chamber and, more importantly, contains low levels of microorganisms that can irritate nasal passages or, in rare cases, cause serious infections. Ohio State Health recommends distilled or sterile water for any home medical device, including humidifiers and neti pots.
The same logic applies to appliances and equipment. Steam irons and garment steamers last longer with distilled water because mineral buildup clogs their vents. Lead-acid batteries require distilled water to maintain proper chemistry. Laboratory work and pharmaceutical manufacturing depend on water free of dissolved solids that could interfere with results or formulations.
What Distillation Doesn’t Remove
Distillation is excellent at stripping out minerals, metals, bacteria, and most dissolved solids. But it has a blind spot. Organic compounds with boiling points lower than water’s, such as benzene and toluene, evaporate right along with the steam and end up in the final product. Most home distillers address this with a carbon filter on the output side, but it’s worth knowing that distillation alone doesn’t guarantee removal of every possible contaminant. Volatile organic chemicals are the main exception.
Choosing Between Them
For everyday drinking, tap water in a regulated U.S. system provides minerals your body uses, fluoride your teeth need, and a taste most people prefer. It costs a fraction of a cent per gallon. Distilled water is the right tool for specific jobs: medical devices, sensitive appliances, and any application where dissolved solids cause damage or contamination. If you prefer the purity of distilled water for drinking, consider using mineral-rich tap water for cooking to reduce nutrient losses from food, and talk to your dentist about fluoride supplementation.