Boiling faucet water is a common practice used globally to purify drinking water. The process of heating water to its boiling point is a traditional method, but its effectiveness depends on the type of contaminant present. Understanding what boiling does, and what it does not do, is necessary to determine if it is the right purification method for a specific water supply.
How Boiling Eliminates Biological Threats
Boiling water is highly effective because the sustained high temperature rapidly kills or inactivates waterborne microorganisms. The heat disrupts the internal structures of disease-causing organisms like bacteria, viruses, and protozoa, which are collectively known as pathogens. This process, called thermal denaturation, causes the proteins and enzymes within the microbes to unfold and lose their function, preventing them from surviving or reproducing.
Waterborne pathogens such as E. coli, Vibrio cholerae, and Hepatitis A virus are destroyed at temperatures well below the boiling point. Even hardier organisms like the protozoan cysts of Giardia and Cryptosporidium, which resist standard chemical disinfection, are rendered harmless by the high heat. Reaching a full, rolling boil ensures that all common biological threats are eliminated. This makes boiling a reliable disinfection method, particularly in emergency situations or when the water source is biologically compromised.
Contaminants Boiling Does Not Remove
While boiling is excellent for biological purification, it is ineffective against chemical contaminants and dissolved solids. Substances such as heavy metals, nitrates, and pesticides are heat-stable and remain in the water even after boiling. Common heavy metals like lead, arsenic, and mercury have boiling points significantly higher than water, meaning they will not evaporate with the steam.
Boiling can actually increase the concentration of these non-volatile contaminants in the remaining liquid. As the water evaporates, the harmful substances are left behind in a smaller volume, potentially making the water more dangerous than before it was boiled. If the water contains high levels of lead, boiling the water will concentrate the lead, increasing the risk of exposure.
Boiling can also increase the presence of certain volatile organic compounds (VOCs), which have lower boiling points than water. While some VOCs will evaporate, others may react or become more concentrated, posing a chemical risk. Therefore, relying on boiling alone for water suspected of chemical contamination, such as industrial runoff or high nitrate levels, is not a safe solution.
The Correct Way to Boil Water for Consumption
When biological contamination is suspected, boiling water must be done correctly to ensure safety. If the water is cloudy or contains visible sediment, it should first be filtered through a clean cloth, paper towel, or coffee filter to improve clarity. Filtering the water removes turbidity, which can interfere with the disinfection process.
The water must then be brought to a full, rolling boil, defined as vigorous and continuous bubbling. This boil should be maintained for at least one full minute at elevations below 6,500 feet. At higher elevations, where water boils at a lower temperature, the duration must be extended to three full minutes to achieve proper disinfection.
After boiling, allow the water to cool naturally without adding ice or mixing it with unboiled water, which could cause recontamination. Store the cooled water in clean, tightly covered containers to prevent new pathogens from entering. Properly boiled and stored water is safe for drinking, cooking, washing produce, and mixing baby formula.
Situations Where Boiling is the Recommended Solution
Boiling is the immediate and most reliable method for making water microbiologically safe when biological contamination is high. The most common situation is during a public health “boil water advisory” issued by municipal authorities. These advisories follow events like a water main break, a drop in water pressure, or a failure in the water treatment system, which allow pathogens to enter the supply.
Boiling is also the recommended solution in emergency preparedness scenarios, such as after a flood, natural disaster, or power outage, where the integrity of the water system is unknown. Travelers and campers using water from an untreated source, such as a lake or stream, should rely on boiling to eliminate naturally occurring bacteria and parasites. If a “Do Not Drink” advisory is issued, it usually signifies chemical contamination, and boiling the water will not make it safe.