The question of whether boiled water is identical to distilled water is common, as both purification methods involve heat. Despite this shared initial step, the two resulting forms of water are fundamentally different in composition and purity. Boiling water makes it safe from biological threats, but distillation physically separates the water molecule from nearly all contaminants. Understanding the specific effects of each process clarifies why they serve entirely different purposes, from emergency sanitation to high-precision laboratory work.
How Boiling Water Alters Water Composition
Boiling water is a simple, centuries-old method of making a water source microbiologically safe for consumption. The process involves heating water to its boiling point of 212°F (100°C) for a recommended period, often one to three minutes. This high temperature is highly effective at inactivating or killing pathogenic organisms, including bacteria, viruses, and protozoan cysts.
This thermal disinfection does not alter the chemical composition of the water or remove non-biological contaminants. Dissolved inorganic substances, such as minerals, salts, and heavy metals, have boiling points far exceeding that of water and remain in the boiling vessel. As some water turns into steam and evaporates, the concentration of total dissolved solids (TDS) actually increases in the remaining liquid. While boiled water is sanitized, it is still chemically the same as the source water, only slightly more concentrated with its original impurities.
The Science of Distillation
Distillation is a physical separation process that achieves a far greater degree of purity than simple boiling. The method involves heating the source water past its boiling point to create steam, which is essentially pure water vapor. This steam is channeled away from the original liquid into a separate cooling chamber, where it condenses back into a liquid state. The resulting liquid, collected in a clean container, is known as distilled water.
The fundamental principle of distillation is that the phase change from liquid to gas leaves behind virtually all non-volatile substances. Inorganic contaminants like calcium, magnesium, sodium, nitrates, and heavy metals are unable to vaporize with the water and are left as residue in the boiling chamber. This two-step process of vaporization and condensation removes up to 99.5 percent of impurities, resulting in water that is very close to pure H2O.
Comparing the Final Products
The most significant difference between the two products lies in their Total Dissolved Solids (TDS) content, which measures inorganic and organic material dissolved in the water. Boiled water retains the entire TDS profile of the source water. For example, a source with 500 parts per million (ppm) of dissolved solids will still have a comparable, or slightly higher, TDS level after boiling.
Distilled water, conversely, has a TDS measurement approaching zero, often less than 10 ppm, due to the physical separation of water from its dissolved contents. This mineral-free state is its defining characteristic, setting it apart from all other common water types. Its goal is chemical purity, which is why it is classified as purified water. A minor limitation is that volatile organic compounds (VOCs), which have boiling points similar to water, can sometimes vaporize and carry over into the final product.
Practical Uses for Each Type of Water
The distinct compositions of the two types of water dictate their appropriate applications. Boiled water is primarily intended for consumption, particularly when the water source is questionable or under a “boil water” advisory. Because boiling preserves the dissolved minerals, the water retains a familiar taste, and minerals like calcium and magnesium are still present.
Distilled water is mandated for applications where the absence of minerals is paramount, as mineral buildup can cause damage or interfere with processes. This includes use in medical devices, such as Continuous Positive Airway Pressure (CPAP) machines, to prevent scale formation in the humidifier. Because distilled water is devoid of dissolved gases and minerals, many people find it tastes “flat” or “bland” compared to tap or boiled water.
It is also the preferred choice for several technical and scientific applications:
- Automotive cooling systems.
- Lead-acid batteries.
- Steam irons.
- Scientific laboratories, where mineral-free water is necessary for accurate results.