Boiling water is a long-standing and widespread practice for making questionable water safe to drink. This process applies heat to eliminate biological contaminants that can cause illness. Boiling is considered a highly effective method of disinfection against harmful microorganisms, making it a reliable technique when the safety of a water source is uncertain.
How Boiling Kills Pathogens
The effectiveness of boiling water stems from its ability to destroy the cellular components of living organisms through thermal energy. When water reaches high temperatures, the heat causes the proteins within microorganisms to denature, or lose their functional structure. This structural damage disrupts the essential life processes of the pathogen, preventing it from reproducing or causing infection.
Boiling is a method of pasteurization, specifically intended to inactivate disease-causing agents. This thermal destruction is highly effective against waterborne biological threats, rapidly eliminating bacteria (such as E. coli and Salmonella) and viruses (including Hepatitis A and Rotavirus). Even hardier organisms, such as protozoan cysts like Giardia and Cryptosporidium, are reliably inactivated by the heat.
Studies show that many waterborne pathogens are killed at temperatures well below the boiling point of 212°F (100°C). However, bringing water to a full rolling boil is the standard practice because it offers visual assurance that the necessary disinfecting temperature has been reached across the entire volume of water.
Contaminants Boiling Does Not Address
While heat successfully eliminates biological threats, boiling does not remove non-biological contaminants, which is a significant limitation. Chemical pollutants, such as pesticides, industrial solvents, and pharmaceuticals, are often heat-stable and are not neutralized by the boiling process. These substances remain in the water, posing a potential health risk.
Heavy metals, including lead, arsenic, and mercury, are a major concern because they have much higher boiling points than water. Consequently, they do not evaporate and are left behind in the remaining liquid. As the water volume decreases due to evaporation, the concentration of these dissolved contaminants can actually increase, potentially making the post-boiled water more hazardous.
Boiling water also does not remove salts or minerals, such as nitrates and fluoride. If a water source has high levels of dissolved solids, boiling will intensify their presence, possibly altering the taste and mineral content. Water that appears cloudy or turbid due to suspended dirt or sediment needs separate treatment, as these physical particles are not removed by boiling and can interfere with disinfection.
Step-by-Step Guide for Safe Boiling
The initial step in preparing water for boiling involves addressing any visible cloudiness or sediment. If the water is not clear, it should first be filtered through a clean cloth, paper towel, or coffee filter to remove suspended solids. Alternatively, the water can be allowed to settle, with only the clearer water from the top drawn off for treatment.
Next, the water must be brought to a full, rolling boil on a heat source. For most people at lower elevations, maintaining this vigorous boil for one minute is sufficient to inactivate pathogens. If you are at an altitude above 6,500 feet (about 2,000 meters), the boiling temperature is lower, and the recommended time is extended to three minutes to provide an equivalent level of safety.
After boiling, the water should be allowed to cool naturally before consumption. To prevent recontamination, the treated water must be stored in clean, sanitized containers with tight-fitting covers. If the boiled water has a flat taste due to the removal of dissolved gases, pouring it back and forth between two clean containers several times can help aerate it and improve the flavor.