Boiling water is the oldest and most reliable technique for emergency water purification, a necessity when a water source is compromised or unknown. Boil water advisories, emergency situations, or travel to areas with uncertain water quality often require this method to ensure safety. This simple act of heating water effectively addresses biological contamination, the most common cause of waterborne illness. Understanding the correct procedure is important for making water safe to drink.
Standard Guidelines for Boiling Water
The core requirement for purifying water with heat is to achieve a rolling boil—a vigorous, continuous bubbling that cannot be stopped by stirring. This ensures the entire volume of water has reached the necessary temperature for disinfection. At sea level, water boils at 212°F (100°C), and the standard instruction is to maintain this rolling boil for a minimum of one minute to inactivate harmful pathogens.
The required boiling time changes significantly as altitude increases because atmospheric pressure decreases. For elevations above 6,500 feet (approximately 2,000 meters), water boils at a lower temperature, which necessitates a longer exposure time to heat. The Centers for Disease Control and Prevention recommends extending the boiling time to at least three minutes at these higher altitudes to compensate for the reduced heat. Once the boiling time is complete, the water must be allowed to cool naturally before consumption.
How Heat Eliminates Contaminants
Boiling works by a process called thermal inactivation, which targets the cellular structure of biological pathogens. The high temperatures achieved during boiling are sufficient to denature the proteins and enzymes essential for the survival and reproduction of microorganisms. This heat exposure effectively destroys bacteria, such as E. coli and Salmonella, as well as viruses and protozoa like Giardia and Cryptosporidium, which are common causes of waterborne disease.
Heating water to a rolling boil is considered a form of pasteurization, which kills a high percentage of disease-causing organisms. This process only addresses biological threats and does not remove chemical contaminants. Boiling water does not eliminate heavy metals, pesticides, or other stable chemical pollutants, which remain in the water, sometimes in a more concentrated form due to water evaporation. Therefore, boiling makes the water biologically safe, but it does not guarantee the removal of non-biological impurities.
Handling and Storage After Boiling
After boiling, the water must be allowed to cool without introducing new contaminants. Allowing the water to cool naturally within the same clean pot or container is the best practice. If the raw water was visibly cloudy or contained sediment, it should have been strained through a clean cloth or coffee filter before boiling. Alternatively, allowing the sediment to settle after boiling, and then carefully pouring off the clearer water, can help improve the water’s appearance.
For storage, the purified water must be transferred into clean, sanitized, food-grade containers with airtight lids. Containers should be thoroughly washed with soap and hot water before use. To maintain safety, the stored water should be clearly labeled as “purified” along with the date, and kept in a cool, dark place away from potential sources of contamination. The taste of boiled water, which can sometimes seem flat, may be improved by pouring it back and forth between two clean containers to reintroduce air.