Distilled water is often considered the standard for purity, leading many people to wonder if this process is effective against the emerging threat of per- and polyfluoroalkyl substances (PFAS). These so-called “forever chemicals” have become a widespread concern due to their persistence in the environment and their presence in many municipal water supplies. Understanding the science behind distillation and the unique nature of PFAS is the only way to determine if distilled water can reliably deliver water free of these contaminants. This explanation will detail the chemical properties of PFAS and how the physical process of distillation provides a highly effective solution for their removal.
Understanding PFAS Chemical Properties
PFAS represent a large family of thousands of synthetic compounds, all characterized by a strong carbon-fluorine bond that makes them extremely stable. This bond is one of the strongest in organic chemistry, which is why these substances resist chemical and thermal degradation, earning them the nickname “forever chemicals.” This chemical robustness means that standard boiling or conventional water treatments are often ineffective at breaking them down. The properties of PFAS most relevant to purification are their thermal stability and non-volatility. Most PFAS compounds have boiling points significantly higher than the boiling point of water, which is 100 degrees Celsius (212 degrees Fahrenheit). Due to these high boiling points, the vast majority of PFAS are considered non-volatile, meaning they do not easily vaporize when water is heated.
How Distillation Separates Contaminants
Distillation is a physical separation technique that mimics the natural hydrologic cycle by exploiting the difference in boiling points between water and its impurities. The process involves heating contaminated source water in a boiling chamber until it turns into steam. This vapor is then collected and cooled in a separate condenser, returning it to its liquid form as purified water. The fundamental principle is that non-volatile contaminants, such as heavy metals, salts, minerals, and most synthetic chemicals, have boiling points far exceeding that of water. Because they are unable to vaporize at water’s boiling temperature, these substances are left behind in the boiling chamber as a concentrated residue.
The Efficacy of Distillation for PFAS Removal
Distillation is highly effective at removing the vast majority of PFAS because their non-volatile chemical properties prevent them from vaporizing with the steam. These compounds remain physically trapped in the boiling reservoir while the water molecules change phase into gas. Laboratory testing has demonstrated that high-quality water distillers can remove well over 99% of all PFAS, including common types such as PFOA and PFOS. This high removal rate is directly attributable to the large difference between the boiling point of water and the boiling points of most PFAS. However, a minor theoretical risk known as “carryover” exists if the water is boiled too vigorously, causing tiny liquid water droplets to splash into the condenser; additionally, some short-chain PFAS are slightly more volatile, allowing trace amounts to potentially pass into the distillate.
Post-Purification Contamination Risks and Alternatives
Storage Risks
Even after effective distillation, the purified water faces a risk of re-contamination before consumption. Distilled water is highly pure and acts as a powerful solvent, meaning it can readily leach substances from its storage container. If the distilled water is stored in certain plastics, chemicals from the container could potentially leach into the water over time. Storing the final product in containers made of glass or high-grade, non-leaching materials is recommended to maintain its purity.
Alternatives to Distillation
When comparing distillation to other common household methods, it proves to be one of the most reliable options for non-volatile contaminants. Reverse Osmosis (RO) systems are also extremely effective, using a semi-permeable membrane to achieve high removal rates for both long- and short-chain PFAS. Granular Activated Carbon (GAC) filters adsorb the chemicals, performing best with long-chain PFAS but often struggling with the smaller, short-chain varieties. Distillation’s physical phase change provides a robust separation mechanism that is highly effective across a broad spectrum of non-volatile impurities, placing it among the top choices for consumers seeking a high level of water purification from PFAS.