Boiling water is an effective method for making water safe to drink, especially during emergencies or when water quality is uncertain. It primarily works by eliminating harmful microorganisms.
The Science Behind Boiling Water Purification
Boiling water purifies it by exposing microorganisms to high temperatures, which damages their cellular structures and proteins. This process, known as heat denaturation, renders bacteria, viruses, and parasites inactive or dead. Boiling is not sterilization, which kills all organisms, but rather pasteurization, targeting and eliminating pathogens that cause human illness.
This heat treatment is highly effective against common waterborne pathogens, including bacteria like Escherichia coli (E. coli), Salmonella, and Vibrio cholerae, as well as protozoa such as Giardia lamblia and Cryptosporidium parvum. Viruses like Hepatitis A and rotaviruses are also inactivated by boiling temperatures. While some bacterial spores, such as certain Clostridium and Bacillus species, can survive boiling, these are generally not waterborne pathogens that cause illness through ingestion.
Recommended Boiling Times for Safety
To effectively kill most waterborne pathogens, bring water to a “rolling boil” and maintain it for a specific duration. A rolling boil means vigorous, continuous bubbling throughout the water.
For elevations up to 6,500 feet (approximately 2,000 meters), boiling water for one minute is sufficient to inactivate bacteria, viruses, and protozoa. At higher altitudes, water boils at a lower temperature due to decreased atmospheric pressure. To compensate for this lower boiling temperature and ensure effective pathogen inactivation, the recommended boiling time increases to three minutes for elevations above 6,500 feet. While water reaches boiling point faster at higher altitudes due to reduced energy requirements, the lower temperature means it takes longer to achieve the same level of disinfection.
What Boiling Water Does Not Remove
While boiling is effective at eliminating biological contaminants, it has limitations regarding other types of impurities. Boiling does not remove chemical pollutants like pesticides, herbicides, or industrial solvents, as these are unaffected by heat.
Heavy metals like lead, mercury, and arsenic are also not removed by boiling. In fact, as water evaporates, their concentration can increase in the remaining water, potentially making it more hazardous.
Boiling also does not eliminate salts, minerals, or particulate matter like sediment and dirt. Therefore, while boiling purifies water from living organisms, it is not a method for filtration or chemical decontamination.
Practical Steps for Boiling and Safe Storage
To correctly boil water for consumption, use a clean pot. If the water appears cloudy, filter it first through a clean cloth or coffee filter to remove sediment.
Place the pot on a heat source and bring the water to a full, rolling boil. Maintain this vigorous boil for the recommended duration: one minute at elevations up to 6,500 feet, or three minutes at higher altitudes.
After boiling, allow the water to cool completely before use. Store the purified water in clean, sanitized, food-grade containers with tight-fitting covers to prevent recontamination. Avoid touching the inside of the container or the water with your hands during transfer. Storing containers in a cool, dark place, away from direct sunlight and chemicals, helps maintain water purity.