Boiling tap water is a common question, especially during water advisories or when the quality of a source is unknown. Boiling is a straightforward, accessible method for treating water, often serving as a first line of defense against potential hazards. This process is highly effective for eliminating certain threats, but it offers no protection against others. Understanding the limitations and proper procedure is important for safely treating water in an emergency.
Boiling Eliminates Pathogens
Boiling water is an effective way to neutralize biological contamination, including disease-causing microorganisms like bacteria, viruses, and protozoa. The high temperature physically destroys the cellular components of these pathogens by causing the denaturation of proteins.
This mechanism is why a boil water notice is typically issued following events like a water main break or a flood, where the risk of microbial contamination is high. The heat successfully inactivates nearly all waterborne pathogens, including common culprits such as E. coli, Salmonella, Hepatitis A virus, and the hardy cysts of Giardia and Cryptosporidium.
Achieving a full, rolling boil is the standard recommendation because it ensures the water has reached 212°F (100°C) at sea level. This temperature threshold is sufficient to eliminate the infectious agents that cause waterborne illnesses. Boiling is a reliable disinfection method when biological threats are the primary concern.
Contaminants That Remain After Boiling
While boiling excels at disinfection, it is ineffective against a wide array of chemical and heavy metal contaminants found in water. These substances are not biological and are not destroyed by heat. In fact, boiling often causes these non-volatile contaminants to become more concentrated in the remaining water.
Heavy metals, such as lead, arsenic, and mercury, do not evaporate when water reaches its boiling point. If these metals are present, boiling causes some of the pure water to turn to steam. This leaves a smaller volume of water with the same amount of metal, thereby increasing the concentration of the harmful substance intended for drinking.
Other dissolved solids and chemical pollutants, including nitrates and certain pesticides, also remain unaffected by the heat. Nitrates, often found in well water due to agricultural runoff, are highly soluble and do not break down at 212°F. Pharmaceuticals and “forever chemicals” known as PFAS are similarly heat-stable compounds that persist through boiling. Relying on boiling alone in situations involving chemical spills or industrial contamination will not make the water safe.
Practical Steps for Water Purification
Before beginning the boiling process, first filter the water if it appears cloudy or contains visible sediment. Passing the water through a clean cloth, paper towel, or coffee filter helps remove debris. Starting with clear water ensures the heat can reach all parts of the liquid efficiently.
Once the water is in a clean pot, bring it to a full, rolling boil. This vigorous boiling action should be maintained for a minimum of one minute to neutralize all microbial contaminants. If you are above 5,000 feet (about 1,500 meters), the boiling duration should be extended to three minutes to compensate for the lower boiling temperature.
After boiling, allow the water to cool naturally without adding ice made from untreated water, which could reintroduce pathogens. Transfer the purified water to a clean, sealed container with a tight-fitting lid to prevent recontamination. If the boiled water tastes flat due to the loss of dissolved oxygen, pouring it back and forth between two clean containers will help to aerate it and restore a more palatable flavor.