The difference between tap water and distilled water is fundamentally a matter of origin and chemical composition. While both are primarily H₂O, tap water is a complex solution containing dissolved substances, whereas distilled water is nearly pure water. The source and treatment dictate the water’s final profile, leading to drastically different uses and physiological effects. Understanding these distinctions is important for making informed choices about consumption and application.
Tap Water: Source and Composition
Tap water originates from natural sources like surface water and groundwater before undergoing municipal treatment. This treatment typically involves multiple steps, including coagulation, sedimentation, and filtration to remove particulate matter, followed by disinfection using chlorine or chloramine to eliminate harmful microorganisms. In many regions, regulated chemicals such as fluoride are intentionally added to promote dental health.
The defining characteristic of tap water is the presence of naturally occurring dissolved solids, including minerals picked up from the surrounding soil and rock formations. These minerals often include calcium, magnesium, and potassium, which contribute to the water’s “hardness.” The exact chemical profile is highly variable, depending on the source area and local regulatory standards. Municipal systems ensure that regulated contaminants remain below established safety thresholds, making the water safe for general consumption.
Distilled Water: Purification Process and Purity
Distilled water is created through a purification method that mimics the natural hydrologic cycle. The process involves heating water to its boiling point, turning it into steam, and then condensing the steam back into a liquid form in a separate collection vessel. This phase change is highly effective because water vaporizes at a lower temperature than most contaminants and dissolved solids.
As the water turns to vapor, it leaves behind virtually all non-volatile substances, including minerals, salts, heavy metals, and most microorganisms. The resulting liquid is exceptionally pure, often removing upwards of 99.5% of dissolved impurities. However, compounds with boiling points lower than water, such as certain volatile organic compounds (VOCs), may vaporize along with the water and require additional filtration to be fully removed.
Practical Differences in Use and Taste
The chemical purity of distilled water makes it necessary for specific technical applications but unsuitable for many everyday uses. Tap water, containing dissolved minerals, has a taste profile influenced by those solids, often described as refreshing. In contrast, distilled water tastes “flat” or “bland” because the complete absence of dissolved minerals or gases removes the elements that give water its customary flavor.
Distilled water’s lack of dissolved solids is required in applications where mineral buildup would cause damage or interfere with processes. It is the standard choice for use in Continuous Positive Airway Pressure (CPAP) machines and steam irons to prevent mineral scale from forming and clogging the equipment. It is also the preferred medium for laboratory experiments, automotive batteries, and medical equipment cleaning, where the introduction of trace ions or contaminants must be avoided. Tap water is the default choice for all general domestic purposes like drinking, cooking, and cleaning.
Health Implications of Consumption
The primary difference in the health implications of the two water types lies in their mineral content. Tap water is a minor source of dietary minerals, providing small amounts of essential nutrients like calcium and magnesium. The safety of tap water is overseen by regulatory bodies, ensuring it is a reliable and safe source of hydration.
Distilled water, lacking these minerals, is not recommended for long-term, primary consumption. Its extremely low mineral content and hypotonic nature mean that when consumed, it can be “aggressive,” potentially causing the body to excrete more minerals than normal to maintain osmotic balance. Long-term consumption of demineralized water may lead to a deficiency in electrolytes, which can manifest as fatigue, weakness, or muscle cramps, according to the World Health Organization. While drinking distilled water in the short term is generally safe if the diet is rich in minerals, it is not an optimal source for continuous daily hydration.