Understanding the Distillation Process
Distillation is a water purification method that mimics the natural hydrologic cycle, but in a controlled environment. The process is a physical separation that relies on a phase change to separate water molecules from most other substances. The core principle is that water has a specific boiling point (100°C or 212°F at sea level), while most contaminants, such as minerals, salts, and heavy metals, have significantly different, often higher, boiling points.
How Distillation Works
- Boiling: The raw water, containing various impurities, is heated in a boiling chamber. As the temperature rises, the water begins to vaporize and turns into steam.
- Separation: Non-volatile impurities—those with boiling points higher than water—are left behind in the boiling chamber. This includes dissolved minerals, salts, and large organic compounds. The intense heat also effectively kills microorganisms like bacteria, viruses, and protozoa.
- Condensation: The rising steam, now free from these non-volatile contaminants, moves into a separate, cooled chamber called a condenser. Here, the temperature drops, and the steam reverts to a liquid state, forming pure water droplets.
- Collection: The newly formed pure water, or "distillate," is collected in a clean storage container. Some modern distillers also incorporate a post-filtration step, often using an activated carbon filter, to remove any remaining trace volatile organic compounds (VOCs) that may have vaporized with the water.
Chemicals Removed in Distilled Water
Distillation is highly effective at removing a broad spectrum of chemicals and contaminants. The principle of separating based on boiling points means that most inorganic compounds and many organic ones are left behind.
Inorganic Contaminants
The most commonly known chemicals removed by distillation are inorganic minerals and salts. These do not vaporize with the steam and are left as residue in the boiling chamber. This includes:
- Hardness minerals: Calcium and magnesium, which cause limescale buildup, are effectively removed.
- Heavy metals: Lead, mercury, arsenic, chromium, and cadmium, all of which are potential health hazards, are left behind due to their high boiling points.
- Fluoride: Unlike many other purification methods, distillation removes fluoride, which is often added to tap water supplies.
- Nitrates: These inorganic compounds, which can be harmful to infants, are also removed during the process.
- Sodium: Distillation is an effective way to remove sodium and other salts from water, a process used in desalination.
Organic Contaminants
Many organic compounds are also removed, though effectiveness can vary depending on their boiling points. The high temperatures can kill or eliminate many biological contaminants, but some volatile organic compounds (VOCs) with boiling points near or below water's boiling point can pose a challenge. This is where an additional filtration step is crucial.
Organic contaminants effectively removed:
- Pesticides (most types)
- Bacteria and Viruses
- Protozoa and Cysts (like giardia)
- Large non-volatile organic molecules
Organic contaminants that may carry over (VOCs):
- Benzene
- Toluene
- Methane
- Some solvents
To counter this, many modern distillers employ an activated carbon filter at the end of the process to adsorb any lingering VOCs, ensuring a high level of overall purity.
Distillation vs. Reverse Osmosis
While both distillation and reverse osmosis (RO) are effective water purification methods, they operate on different principles and have distinct advantages and disadvantages. This table compares the two methods.
| Feature | Distillation | Reverse Osmosis (RO) |
|---|---|---|
| Principle | Heats water to steam, then condenses it back to liquid, leaving impurities behind based on boiling point differences. | Forces water under pressure through a semi-permeable membrane that blocks impurities based on molecule size. |
| Contaminant Removal | Removes a very broad range of contaminants, including minerals, heavy metals, and microorganisms. May require additional filtration for VOCs. | Removes most dissolved solids, salts, and minerals. Less effective at removing smaller volatile compounds, like some pesticides and solvents. |
| Purity Level | Produces exceptionally high-purity water, often approaching 99.9%. | Also produces high-purity water, but mineral content can be slightly higher depending on the system's efficiency. |
| Energy Consumption | High, due to the energy required to boil water. | Lower, as it uses pressure rather than heat. |
| Processing Speed | Slower, as it is a batch process reliant on evaporation and condensation rates. | Faster, and can be configured for continuous flow. |
| Water Waste | Minimal water waste, though some water remains in the boiling chamber with concentrated impurities. | Significant water waste (brine) is produced, which must be discarded. |
| Cost | High operational cost due to energy, but durable equipment. | Lower operating costs, but ongoing expense for filter and membrane replacement. |
Health and Taste Considerations
One of the most noticeable side effects of removing all minerals and dissolved solids is a change in taste. Because distilled water lacks the trace minerals that give tap water its characteristic flavor, many people describe it as tasting "flat" or "bland". For applications where a specific taste is not required, such as in laboratory experiments, this is not an issue.
From a health perspective, the removal of beneficial minerals like calcium and magnesium has led to some debate about whether distilled water is healthy for long-term consumption. However, it is important to note that tap water is not the primary source of these nutrients for most people, who get them through a balanced diet. For those with certain medical conditions or in areas with very poor water quality, the safety benefits of contaminant removal may outweigh the loss of minerals.
Practical Applications of Distilled Water
The exceptional purity of distilled water makes it suitable for a wide range of applications where mineral content or contamination could cause problems. These uses include:
- Automotive: Used in car batteries and cooling systems to prevent mineral buildup and corrosion.
- Medical and Laboratory: Used for sterilizing equipment, in lab testing, and in various medical procedures that require high-purity water to prevent interference.
- Appliances: Recommended for use in steam irons and humidifiers to prevent limescale and mineral deposits that can damage the device.
- Cosmetics and Skincare: Used in manufacturing to ensure product stability and avoid contamination.
For more information on water quality testing and treatment options, consult trusted resources like the Environmental Protection Agency (EPA) or a reputable university extension program.
Conclusion
Distillation is a robust and highly effective method for producing extremely pure water by removing a wide range of contaminants, including inorganic minerals, salts, heavy metals, and most microorganisms. It works by exploiting the difference in boiling points, leaving behind impurities as water vapor is collected and condensed. While it creates water with a flat taste and removes beneficial minerals, its high purity makes it ideal for many industrial, medical, and household applications where the presence of dissolved solids is undesirable. Understanding what chemicals are removed in distilled water is crucial for determining if it is the right purification method for a specific need.
