Boiling tap water is a traditional and highly effective method for disinfection, often used when the safety of a water supply is uncertain. This simple practice, requiring only a heat source and a container, is a common response during emergencies or when public water quality is compromised. Whether boiling makes tap water safe is nuanced, depending on the specific contaminants present in the water supply. While boiling is a powerful tool against biological threats, it is entirely ineffective against many chemical pollutants. Understanding what boiling removes and what it does not is essential for ensuring your drinking water is truly safe.
How Boiling Eliminates Biological Threats
Boiling water functions as an effective form of pasteurization, utilizing heat to deactivate or kill pathogenic microorganisms that cause waterborne diseases. The high temperature damages the structural components of these organisms, disrupting essential life processes and denaturing the proteins necessary for survival. This process is highly successful against bacteria like E. coli and Salmonella, viruses, and protozoa.
Protozoan cysts, such as Giardia and Cryptosporidium, are reliably inactivated even at temperatures well below the boiling point. Heating water to 149°F (65°C) for five minutes achieves a near-complete kill of waterborne microorganisms. Boiling is the primary reason public health authorities issue a “boil water advisory” when infrastructure disruptions could introduce microbes.
Contaminants Boiling Does Not Remove
Boiling is limited exclusively to biological contaminants and offers no protection against non-volatile chemical pollutants. Substances that do not evaporate easily, such as heavy metals like lead and arsenic, remain in the water even after prolonged boiling. Inorganic chemicals like nitrates, fluoride, and pesticides are similarly unaffected by the heat.
The act of boiling can unintentionally increase the concentration of these chemical contaminants. As the water is heated, pure water vaporizes and escapes as steam, leaving non-volatile substances behind in the reduced volume of liquid. This concentration effect means the remaining water can have a higher level of pollutants than it did initially. High levels of concentrated nitrates, for example, are a concern for infants under six months old, as they can cause methemoglobinemia.
Safe Boiling Procedures and Context
Boiling is recommended primarily during official advisories following events like infrastructure failure, floods, or power outages, when the risk of microbial contamination is high. If the tap water appears cloudy or turbid, it should first be filtered through a clean cloth or coffee filter to remove debris before boiling.
To ensure disinfection, water must be brought to a full, rolling boil. At sea level, maintain a rolling boil for at least one full minute. For locations above 6,500 feet (approximately 2,000 meters), the recommended boiling time increases to three minutes. This longer duration compensates for the lower boiling temperature at higher elevations, guaranteeing adequate pasteurization. After boiling, allow the water to cool and store it in clean, covered containers to prevent recontamination.