Boiling tap water is a time-tested household method often used to address concerns about water quality, whether due to a municipal advisory or simply out of caution. This process is a form of thermal disinfection, which leverages high temperatures to make water safe for consumption. While boiling is highly effective against biological threats, it is not a complete purification process. Understanding the true capabilities and, more importantly, the limitations of boiling is necessary to ensure your drinking water is safe from all potential contaminants.
How Boiling Makes Water Safe From Microbes
Boiling water is an excellent method for eliminating waterborne pathogens, a process known as thermal inactivation. When water reaches a rolling boil—which occurs at 212°F (100°C) at sea level—the intense heat rapidly destroys harmful microorganisms. This high temperature denatures the proteins and nucleic acids that are essential for the survival and reproduction of these organisms, rendering them harmless.
The heat is highly effective against bacteria, such as E. coli and Salmonella, as well as viruses like Hepatitis A. Protozoan cysts, including the tough-walled Giardia and Cryptosporidium, are also inactivated by boiling, which is why it is the standard recommendation during a “boil water advisory.” This method acts like pasteurization, neutralizing the germs that cause waterborne illnesses.
Contaminants Boiling Will Not Remove
While boiling is a powerful disinfectant, it does not remove chemical or heavy metal contaminants. These substances have much higher boiling points than water, meaning they remain in the liquid. In fact, as the water evaporates into steam, the concentration of these non-volatile contaminants actually increases in the remaining volume.
Heavy metals like lead, arsenic, and mercury, which can leach into water from old plumbing or natural deposits, are unaffected by the heat and become more concentrated. Similarly, inorganic substances such as nitrates—often originating from agricultural runoff—are not removed and their concentration will rise. Certain organic chemicals, including pesticides, pharmaceuticals, and “forever chemicals” like PFAS, are also heat-stable and persist in the boiled water.
Boiling can partially remove some volatile compounds, such as chlorine, which may evaporate with the steam. However, disinfectants like chloramine, a combination of chlorine and ammonia used in many municipal systems, are more stable and remain in the water. Boiling is therefore not a suitable method for addressing chemical contamination, and in some cases, it can increase the concentration of harmful substances.
Practical Steps for Boiling and Storage
To ensure effective disinfection, bring the water to a full, rolling boil that is clearly visible for at least one minute. If you are at an altitude above 5,000 feet, where water boils at a lower temperature, extend this duration to three minutes. Maintaining the rolling boil ensures the water reaches the necessary pasteurization temperature throughout the entire volume.
Once the boiling time is complete, allow the water to cool naturally before consumption; adding ice or cold water can reintroduce contaminants. Store the cooled water in clean, sanitized, and tightly covered food-grade containers. To counteract the flat taste that often results from the removal of dissolved oxygen, pour the water back and forth between two clean containers to aerate it.