Boiling water is a common practice for making it safe to drink, often leading to the assumption that this process eliminates all types of contaminants, including various chemicals. While heating water to its boiling point is effective against certain impurities, this method does not universally purify water from chemical contamination. This article explores what happens when water boils and why it is not a comprehensive solution for removing most chemical substances.
What Happens When Water Boils
When water is heated to its boiling point (100 degrees Celsius/212 degrees Fahrenheit at sea level), it undergoes a phase change from liquid to gas, forming steam. This heat primarily inactivates or kills microorganisms. Pathogenic bacteria, viruses, and parasites cannot survive these high temperatures. Boiling water for at least one minute (or three minutes at altitudes above 2,000 meters/6,500 feet) is recommended to make water microbiologically safe. This process reduces the risk of waterborne diseases.
Why Boiling Doesn’t Remove Most Chemicals
Boiling water does not remove most chemical contaminants, due to their different physical properties. Many inorganic compounds, such as heavy metals like lead and arsenic, have higher boiling points than water or are non-volatile. They do not evaporate with the water, remaining in the vessel. As water boils and converts to steam, its volume decreases, increasing the concentration of these chemicals in the remaining liquid.
Dissolved salts and minerals (e.g., sodium, calcium, magnesium) also remain when water boils. These contribute to water hardness and are not removed. Many persistent organic pollutants (e.g., pesticides, pharmaceuticals) are heat-stable and do not volatilize at water’s boiling point. Nitrates are another example; boiling can increase their concentration as water evaporates but nitrates do not. Consequently, boiling can lead to a higher concentration of these harmful chemicals, making the water more hazardous.
The Exception: Volatile Organic Compounds
Volatile organic compounds (VOCs) are an exception to the general rule regarding boiling and chemical removal. VOCs, including solvents and chlorine disinfection byproducts like trihalomethanes, have lower boiling points than water. When water containing them is boiled, VOCs evaporate with the steam. This transfers them from the water into the surrounding air, rather than eliminating them.
Releasing VOCs into the air creates an inhalation hazard, especially in poorly ventilated spaces. While boiling might reduce VOC concentration in water, it does not remove them from the immediate environment. This transfer highlights that boiling is not a safe or effective method for purifying water from these contaminants.
Reliable Methods for Chemical Removal
Since boiling is ineffective for most chemical contaminants, other methods are necessary. Distillation involves boiling water and collecting the condensed steam, leaving most impurities (e.g., heavy metals, salts) behind. This effectively separates water from non-volatile substances.
Filtration systems offer various approaches to chemical removal. Activated carbon filters trap chlorine, pesticides, and organic chemicals through adsorption. Reverse osmosis (RO) systems use a semi-permeable membrane to remove dissolved solids, heavy metals, nitrates, and organic compounds. Ion exchange systems remove charged contaminants like hardness minerals or nitrates by exchanging them for less harmful ions. Identifying specific contaminants through water testing and selecting a certified filtration system tailored to those needs is important for ensuring water safety.