Boiling is the most reliable method for making water safe to drink when a supply is compromised due to a natural disaster or a public health advisory. This thermal purification process works by exposing waterborne pathogens to high temperatures, effectively killing bacteria, viruses, and parasitic cysts that cause water-related illnesses. The heat disrupts the cellular structures of these microorganisms, making boiling a highly effective and widely accessible emergency treatment.
Preparing Water Before Boiling
Before applying heat, any visible cloudiness or suspended particles, known as turbidity, must be removed. Boiling only kills pathogens and does not remove physical debris, which can interfere with the disinfection process. Highly turbid water contains particles that can shelter microorganisms, shielding them from the full effects of the heat.
To clarify the water, allow it to sit undisturbed, letting the heavier sediment settle to the bottom of the container. Once the debris has settled, carefully pour or siphon the clearer water into a separate container, leaving the sediment behind. The remaining water should then be strained through fine material, such as a clean cloth, a paper towel, or a coffee filter, to remove finer suspended matter.
Recommended Boiling Times and Altitude Adjustments
The standard time required for purification depends on your elevation, as the boiling point of water changes with atmospheric pressure. At sea level, water boils at 212°F (100°C), and maintaining a rolling boil for one full minute (60 seconds) is sufficient to destroy common waterborne pathogens. This temperature and duration combination inactivates disease-causing agents like Giardia lamblia cysts, Cryptosporidium oocysts, and various bacteria and viruses.
The boiling point of water decreases as altitude increases because there is less atmospheric pressure pushing down on the liquid. For instance, at 5,000 feet above sea level, water boils at approximately 203°F, which is a lower temperature than at sea level. To compensate for this lower heat, the boiling time must be extended.
The recommendation for elevations above 6,500 feet (about 2,000 meters) is to boil the water for three full minutes. This extended duration provides an added margin of safety, accounting for the reduced temperature.
Safe Storage and Handling After Purification
Once the boiling time is complete, the treated water must be allowed to cool naturally without external interference. Avoid adding ice or other cooling materials, as they introduce a high risk of re-contamination. After the water has cooled, pour it into storage containers that are clean, sanitized, and made from food-grade material with airtight covers.
To maintain purity, the containers should be handled hygienically, using clean hands and ensuring that no unpurified tools or surfaces touch the water. It is helpful to label each container with the contents and the date of purification to keep track of your supply. Storing purified water in a cool, dark location away from potential chemical vapors or sunlight will further preserve its quality.
Boiling can sometimes result in a flat taste because the process removes dissolved gases like oxygen. To improve the flavor, the water can be “aerated” by pouring it back and forth several times between two clean containers. Alternatively, adding a very small pinch of salt per quart of water can also help restore a more palatable taste profile.