Boiling tap water is a time-honored method for emergency disinfection, and it is highly effective against microscopic organisms that cause illness. The process uses high heat to eliminate biological contaminants, addressing a major component of water safety. However, true water safety requires the removal of both harmful pathogens and chemical pollutants. Boiling only addresses biological threats and has clear limitations when dealing with chemical contamination.
What Boiling Does to Biological Contaminants
Boiling works by pasteurizing the water, which kills or inactivates most disease-causing microorganisms. This high-temperature exposure damages the structural components and life processes of pathogens, such as denaturing their proteins. Waterborne bacteria, including E. coli and Salmonella, are rapidly eliminated once the water reaches a sufficient temperature.
The heat is also successful against viruses, such as rotavirus and Hepatitis A, and the more robust protozoa and their cysts. Organisms like Giardia and Cryptosporidium, which are often resistant to chemical disinfectants like chlorine, are neutralized effectively by a full rolling boil. This makes boiling the standard for securing microbial safety during a boil water advisory or emergency.
The Limits of Boiling: Non-Biological Threats
The primary limitation of boiling is its inability to remove non-volatile chemical contaminants. Substances such as heavy metals, including lead and arsenic, and inorganic minerals remain in the water even after prolonged boiling. These pollutants have heat-resistant structures, rendering the boiling process ineffective.
Boiling water can significantly worsen chemical contamination by causing a concentration effect. As the water evaporates into steam, the volume decreases, but the dissolved chemical contaminants stay behind. This process increases the concentration of harmful substances like nitrates and heavy metals in the remaining water. This concentration is concerning for substances like nitrates, which pose a health risk for infants.
Step-by-Step Guide for Effective Water Boiling
To effectively disinfect water, the process begins before heating, especially if the water is visibly cloudy. Murky water should first be pre-filtered using a clean cloth or coffee filter to remove sediment and debris. Removing this particulate matter prevents solid particles from shielding microorganisms from the heat.
Next, bring the filtered water to a vigorous, rolling boil, meaning the water is bubbling rapidly and continuously. At sea level, sustaining a rolling boil for one minute is sufficient to destroy waterborne pathogens. At high altitudes, generally above 6,562 feet (2,000 meters), water boils at a lower temperature due to reduced atmospheric pressure. To compensate, the recommended boiling time should be increased to three minutes. Once cooled, the treated water must be stored in clean, covered containers to prevent recontamination.
When Boiling is Not Enough: Supplemental Methods
When water is suspected to contain chemical contaminants, boiling must be supplemented with other purification methods. Physical filtration is an accessible solution; activated carbon filters are effective at removing organic compounds, pesticides, and chlorine, which improves taste and odor. Specialized filters, such as those using ion exchange or reverse osmosis, are needed to target specific chemical threats like heavy metals and nitrates.
Distillation offers a high level of purity by leveraging the phase change of water. This process involves heating the water to create steam, which leaves behind virtually all non-volatile substances, including dissolved minerals and heavy metals. The steam is then collected and condensed back into liquid form, offering a purified product free from most chemical and mineral contaminants.