Distillation is highly effective at removing chlorine from water, offering a proven method for purification. This high removal rate is due to the significant difference in boiling points between water and chlorine. Chlorine is a volatile substance that converts to a gas at a temperature far lower than water’s boiling point. This difference in physical properties allows the distillation process to easily separate the disinfectant from the water.
How Water Distillation Works
Water distillation is a purification process that relies on separating substances based on their different boiling points. The process begins by heating source water until it reaches its boiling point of 212°F (100°C), converting the liquid into steam.
As the water turns into steam, it leaves behind non-volatile contaminants in the boiling chamber. These impurities include inorganic compounds like salts, heavy metals such as lead, and dissolved solids like calcium and magnesium. The steam then rises, carrying only water molecules and any substances that vaporized at or below 212°F.
The pure steam is directed into a separate cooling coil or condenser, where it rapidly cools down. This cooling causes the steam to revert back to a liquid state, a process called condensation. The resulting pure water is collected in a clean container, while the concentrated impurities remain in the original boiling chamber to be discarded.
The Volatility of Chlorine and Chloramines
Distillation’s effectiveness against chlorine stems from the fact that free chlorine has an extremely low boiling point, around -35°F (-37°C). This means that as soon as the water begins to heat toward its boiling point, free chlorine molecules rapidly convert into a gas, a process known as volatilization. By the time the water is actively boiling, nearly all free chlorine has already gassed off alongside the rising steam.
A more complex challenge arises with chloramines, which are increasingly used by municipalities and formed when chlorine is combined with ammonia. Unlike free chlorine, chloramine is a significantly more stable molecule and does not easily volatilize, even when the water is boiling. Simple boiling for short periods is generally insufficient to achieve high chloramine reduction.
Specialized water distillers address the stability of chloramines and other volatile gases through design features like venting. These vents allow the gases, which are lighter than the water vapor, to escape into the atmosphere before condensation occurs. This venting mechanism ensures a much higher removal efficiency for both free chlorine and the more stubborn chloramine compounds. Distillation can eliminate up to 97% of chlorine, often achieving higher rates when the system includes venting or a final-stage carbon filter.
What Distillation Does Not Remove
While distillation is highly effective at removing chlorine and non-volatile substances, it has limitations concerning certain organic compounds. Highly volatile organic compounds (VOCs) are chemicals with boiling points close to or lower than that of water, such as certain pesticides and solvents. These VOCs can vaporize along with the water molecules and potentially re-contaminate the purified water during condensation.
To prevent this carryover, many modern distillation units incorporate a secondary treatment, typically an activated carbon filter, to polish the final product water. This post-filtration step captures any lingering VOCs that were not effectively vented or separated during the boiling stage.
Distillation also removes all natural minerals, such as calcium and magnesium, which are important electrolytes. The resulting water is demineralized, and while pure, it may taste “flat” to some consumers due to the absence of these dissolved solids.