Boiling water is a time-tested technique often used in emergencies or during “boil water” advisories to make questionable water safer to drink. While widely trusted, this method is not a complete purification solution. Its effectiveness depends entirely on the type of contamination present, as boiling only removes certain threats while leaving others behind.
The Primary Benefit: Eliminating Biological Threats
Boiling is highly effective because it acts as a powerful disinfectant against waterborne pathogens. The heat from a rolling boil quickly kills or inactivates disease-causing microorganisms by denaturing their proteins and destroying their cellular structures. Boiling eliminates nearly all harmful microbes, including common bacterial pathogens like E. coli and Salmonella, and waterborne viruses such as Hepatitis A. Boiling is also effective against hardier protozoan cysts, such as Giardia lamblia and Cryptosporidium parvum, which are resistant to chemical disinfectants like chlorine.
Why “Dirty” Water Needs Pre-Treatment
“Dirty” water refers to water with high turbidity, containing suspended particulate matter like mud, silt, and organic debris. Boiling highly turbid water is problematic because these particles can shield microbes from the heat, reducing disinfection effectiveness. Sediment also makes the water unappetizing and difficult to consume. Therefore, highly turbid water must be clarified through pre-treatment before boiling. This step ensures the heat fully penetrates the water and reaches any remaining pathogens.
Pre-Treatment Methods
Pre-treatment involves filtering the water through a clean cloth, paper towel, or coffee filter to remove the largest visible particles. Alternatively, the water can sit for several hours, allowing the sediment to settle to the bottom. The clearer water can then be carefully poured off the top for boiling.
Contaminants Boiling Will Not Remove
Boiling eliminates biological threats but does not remove non-volatile chemical contaminants or dissolved solids. Substances like heavy metals (including lead and arsenic), nitrates, and salts have a much higher boiling point than water. When water boils, the pure water evaporates as steam, leaving these substances behind. This evaporation concentrates the contaminants, potentially increasing their levels in the remaining water. For water sources suspected of having chemical contamination, boiling alone is an inadequate and potentially counterproductive purification method.
Proper Technique for Boiling and Storage
Boiling Technique
To ensure microbial safety, water should reach a full, rolling boil. Maintain the boil for at least one minute at sea level. If you are above 2,000 meters (6,500 feet), increase the boiling time to three minutes, as water boils at a lower temperature at higher elevations. This duration ensures the necessary thermal inactivation of all waterborne pathogens.
Storage and Taste Improvement
After boiling, allow the water to cool naturally while remaining covered to prevent airborne recontamination. Boiled water often tastes flat because the process removes dissolved gases like oxygen. To improve the taste, the water can be aerated by pouring it back and forth between two clean containers, or a small pinch of salt can be added. The purified water must be stored in clean, sanitized, and tightly sealed containers to maintain its safety until consumption.